What is a WebRTC virtual PBX?

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Every type of communication

The best tool for communicating through voice, video, and chat. Your customers will contact your business by phone, or by the Click to Speak button on your website or app. They can also contact you through WhatsApp.


...with full functionality...

In addition to the features of this virtual PBX system, we also offer CRM integration, secure credit card payments over the phone or AI solutions. All with total security thanks to encrypted communications.



...using any device from any location.

Enjoy your modern virtual PBX phone extensions using any internet connected device (computer, cell phone, tablet, etc.) from anywhere in the world, all with HD quality.

A virtual PBX with...everything!

 Choose the best communication tools to reach your customers


International Numbers

Globalize your business with international phone numbers and grow your market presence. Choose phone numbers with foreign country codes to let your global customers know that you are available wherever they are.


The "Click to Speak" button

Offer Click to Speak buttons on your website or business app so that users are able to call you directly from your site without any cost. They can call from anywhere in the world, and through any device all with HD quality.


Local Numbers

Port your current business phone number or choose a new one. Show your national business presence by choosing phone numbers from other provinces. Choose local phone numbers from outside of your city.



Enable WhatsApp to communicate with your customers, close tickets, or talk business. Separate your business WhatsApp account from your personal account. Communicate using separate phone numbers. 

 Add value to your communication systems by adding features to your PBX



Integrate your virtual PBX phone system with your CRM tool to centralize your company and customer data. 


Pay with card

Manage payments through your virtual PBX thanks to the secure PCI-certified telephone card payment system


Add contact center agents

Manage your customer service with our Call Center Software to assist your customers quickly and efficiently.


Control Office Hours

The PBX allows you to control and manage your employees’ schedules and obtain reports to comply with current legislation.


Google Data Studio

Create advanced, personalized interactive reports to analyze and audit your communications in the easiest way.


Atificial Intelligence (AI)

Implement Artificial Intelligence to generate value in the management of your communications and optimize resources.

 Discover the internal communication tools of your virtual PBX


Internal Calls

Talk to any employee, no matter what country they are in. With just one click, you will have unlimited internal business calls, with HD quality and total reliability.


Corporate Chat

Strengthen your company’s internal communication with a corporate chat. Users will be able to chat, create groups, mailing lists, and more. All messages are encrypted.


Video conferencing

Make immediate video conferences with any member of your company. Start video conferences without any installations, from any location and any device, all in HD.

The ultimate features to customize your virtual PBX


Custom main greetings

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Our customized main greetings are informative messages that are heard by callers when they first initially call. They help direct the caller by listing different options based on what they’re looking for. If the caller is making the call outside of business hours, the hours of operation will be listed and different options will guide the caller. Full PBX settings always contain at least four greetings:


This is a welcome message that informs the caller about the company they are calling. For example, “You have reached Fonvirtual.” Depending on the PBX setting, this initial message might need a following step. It may need to guide callers through the different alternatives, such as “If you wish to speak with the accounting department, press 1. For HR, press 2.” 


As a second option, it is always good to add another message that informs callers when all the current phone lines are busy. This allows the caller to decide whether he or she wants to leave a message or try again later.

After hours

For calls made after hours of operation, we recommend including the hours of operation so they know when to call back. For example, “Our customer service hours are from 7 am to 12 pm and from 3 pm to 5 pm.”  You may also want to include the option to leave a voicemail message so you can call them back later.


Lastly, it is also recommended to add a message with holiday hours of operations or office closures to specify when the office will reopen. For example, “Our offices will remain closed today due to the holidays and will reopen again next Wednesday.”

Fonvirtual can set main greetings in TTS (text to speech). Customers with Premium and upgraded subscriptions may include their own messages and human-voice recordings. Fonvirtual will then configure them in your PBX settings.


Call transfer

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When an incoming call enters the PBX system, you may need to transfer that call to another extension without wanting to end the call. With call transferring, the initial extension can now transfer the call to a different extension and will now be available to answer other calls. The Fonvirtual virtual PBX offers two types of Call Transfers:

Attended transfer:

When an incoming call is received, the person who answers it will be able to communicate to other extensions at the same time. That way, they may ask the other person if they are available to answer the call while the caller is placed on hold. The idea is to consult the person who is going to receive the transfer first if they want to accept the call or not. With this feature, you have the choice to either transfer the call to the second line or continue the call now.

Unattended transfer:

This type of call transfer directly routes the call to another extension, without any previous consultation.

For more information about Call Transferring, please send us an email at sales@fonvirtual.com


HD Quality

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The big difference between the rest of IP telephony and WebRTC technology is WebRTC’s HD quality sound and audio.

WebRTC telephony uses an Opus audio codec that is commonly used to play music with very high quality sound. This codec is capable of operating optimally at a wide range of transmission speeds, from 6 kb/s to 510 kb/s and a sampling rate of 8 to 48 kHz. This means that the quality of communication will be optimal with any medium-stable communication. In other words: this codec can move its signal from bitrate narrowband speech to HD stereo sound using the highest quality available.

At a more technical level, a real-time audio codec can be broken into two levels:

  • Linear Prediction (LP) and Code Excited Linear Prediction (CELP), to encode low frequency sound
  • Modified Discrete Cosine Transform (MDCT) to encode music and speech frequencies with higher frequencies

The Opus codec can actively work using both, allowing it to operate over a wider range and achieve better sound quality. Furthermore, the codec can operate with a fixed but also variable bit rate.

It’s clear that the highest level of optimization of this codec will occur in internal communications between extensions and agents, which is also the case with video conferencing. However, we are progressively moving towards the Opus codec having a greater global relevance.



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One of the most useful PBX features is the IVR. This enables the distribution of incoming calls among different departments. That way, the caller is directed to exactly who they’re looking for. For example, the message may sound like this: “If you wish to speak with the accounting department, press 1. For HR, press 2.”

The only thing the caller has to do is press the number that corresponds to what they are calling for. Thanks to IVR, in most cases, we ensure that the call will be answered by the most adequate person first, based on the reason for the call.

There are many ways to divide a particular call. For example, we can direct the call based on department or by language options. For example, “For English, press 1. Para Español, pulse 2,” or by area: “For our New York office, press 1. For our L.A office, press 2.”

Besides it’s many different uses, IVR can also provide a larger company image.


Call queuing

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Call queuing is very useful to companies that may have several incoming calls at the same time. Callers may typically have to wait for a few minutes before their call is answered. In order to avoid callers instantly hanging up the phone, the caller will go into a call queue where they may listen to music while they’re on hold until one of the extensions is no longer busy.

Be aware that callers won’t stay on hold forever. However, having a client on hold helps you win some extra time to finish answering other calls. Plus, having callers on hold helps create an exclusive company image by letting clients know that many people are wanting to contact your company and ask about your excellent services.



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All of our clients have access to their data by simply entering a username and password. By logging in, you will be able to see statistical reports on your call information.

This isn’t just a basic list of incoming calls. Our platform allows you to filter information based on what you’re looking for. With this feature, your search results will generate a report based on all kinds of searchable information, such as specific time frames, call duration, or the origin of each call.

With so many possibilities, your reports will allow you to visualize what areas your company may need to improve on.

For example, if you have an IVR setting, you will be able to see which numbered option is selected the most by your callers, who answers these calls the most or which department has been missing the most calls.

Because of the versatility in data collected through our virtual phone numbers, these statistical reports can be used for launching marketing campaigns or for knowing how many additional virtual numbers should be added to your network in order to grow your business. For more information about our virtual phone numbers, visit the virtual phone number section of our website.


Call recording

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Call recordings are stored as data that you can access later. It is particularly useful for those who are looking for specific things that were said during a conversation, or for those who would like to keep track of who is calling and why.

Call recordings are only available for 10 days, after that they will be permanently deleted from your account. If you would like to keep a copy, you may download them periodically. You can also extend this limited time period by registering for an additional FTP (File Transfer Protocol) service.

For more information about call recording and their legal aspects, please send us an email at sales@fonvirtual.com



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For moments in which you are unable to answer the call, either because you are unavailable, busy or the call was made during after hours, it is crucial to set up a voicemail.

Voicemail gives callers the opportunity to leave a message expressing the reason for their call. With the Fonvirtual voicemail you will immediately receive an email along the lines of “The phone number 64x, xxx, xxxx has tried to contact you at 14:43.”  You will also receive a copy of the voicemail message in an .mp3 format attached to the email.

This feature ensures that you will never miss a call again.



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Downloading and installing any software from the internet, besides being inconvenient and time-consuming, is risky due to the security gaps associated with continuously out-of-date software.

Therefore, unlike traditional IP telephony, this problem does not exist with WebRTC. Because there is no need to install any software, you can communicate directly from any web browser. Your software will always be up to date.

WebRTC always works from any web browser, so any extra security measures are already included in the browser you use, as well as the WebRTC platform. Some security features include:

  • End-to-end encryption between peers
  • Datagram Transport Layer Security (DTLS)
  • Secure Real-Time Protocol (SRTP)

End-to-end encryption

WebRTC’s encryption prevents communication from being tapped or accessed by a third party. This provides a superior layer of security compared to traditional telephone communications, which could be simply hacked, recorded, or manipulated.

Datagram Transport Layer Security (DTLS)

WebRTC’s information and data transfer is performed by the Datagram Transport Layer Security method. This security protocol is compatible with most browsers such as Firefox, Chrome, and Opera. This protocol protects communications and data transferring with a high level of security.

Secure Real-Time Protocol (SRTP)

In addition to DTLS, WebRTC also encrypts information through the Secure Real-Time Protocol that safeguards IP communications from hackers, so that audio and video information remains private.



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The possibility to customize settings based on schedules and calendars is a customer favorite feature. We recommend having at least four different time frames set up for your customer service callers:

Office hours

The main setting should be during your office hours. For example, this setting could be from Monday to Friday, 9 a.m to 2 p.m, and then from 4 p.m to 7 p.m. Withing this time frame, your incoming calls will enter the system so that they may be answered accordingly.

After hours

A second time frame may be the known as “after hours”. Anytime before or after office hours are considered “after hours.” If an incoming call is made during this time frame, callers will hear a list of the correct office hours and to leave a voicemail message.


We find it useful to create a message to inform callers during the holiday season that offices are closed. We recommend creating a setting for each particular holiday. For example, on the 4th of July customers may hear: “Due to Independence Day, our offices are closed today and will reopen again tomorrow”


Finally, if the office will remain closed for an extended period of time, it is convenient to inform clients to not call during that time. For example, the message may sound like this: “Due to a scheduled vacation, our offices will remain closed from July 15th until the 30th.”


Caller ID

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Due to the flexibility of the virtual PBX, professional and personal cell phone numbers may be added from any phone provider as extension. It’s useful being able to identify where a call is originating from, whether it’s from another virtual PBX number in your network or from an outside caller.

If the phone number is coming through a virtual phone number, we can tell in two different ways:

Masked number

A masked number = your virtual phone number. This way, independently of who is calling, you will always see the same phone number; your own. It’s like our own PBX virtual network is the one calling us.

Micro Voice-over

Another alternative is to include a mico voice-over that only you will be able to hear. This means the customer won’t hear it when they’re on the call. This option is especially useful if your company has multiple departments, since you will then know which department the caller trying to reach. For example, if you heard “sales” you would respond differently than if you were to hear “management”. This feature will work the same way if you instead were to answer calls in different languages, such as answering the phone in either English or Spanish.


Other features

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Filter by origin:

Thanks to this feature you will be able to treat calls differently depending on their origin. For example, if you frequently receive foreign calls, the system will enable you to filter calls coming from France and set up a particular greeting in French for those calls.

White lists and black lists:

For clients you want to give special treatment to, there is the white list. They won’t have to wait on hold. They can skip the entire process and be attended to immediately. On the contrary, the black list is for callers you don’t want to receive calls from. This may be spam callers, annoying suppliers, prank callers or irritating telemarketers.  We recommend putting them on the black list so that their calls will no longer be answered. Or, you can choose to put them on an endless hold with repetitive music. Regardless, their calls will never be answered again.

Hunt group and Ring all:

You can also set up a hunt group. With a hunt group, the first extension will always receive the call. Then, if the line is busy or the agent doesn’t pick up the phone, the caller will be transferred to the second extension. This way, the call will pass from one extension to the next until an agent is available to answer the call.

On the contrary, the ring all option calls all available extensions at the same time. The first person to pick up the phone will be the one to answer the call, and then all other available lines will be available for the next call. This is a useful tool when a company receives multiple calls and they want to give equal treatment to all of their incoming callers.

If you know the line, press it:

The Fonvirtual PBX allows callers who already know the extensions of some operators to press it at the beginning of the call to directly contact them, which allows them to skip the normal initial call process.

Message transcription:

Although this feature is currently on a Beta phase, you can receive the transcription of the messages left in your voicemail box via email.

Questions about our service prices?

Your virtual PBX extensions are ubiquitous


On any device

Use your phone extension from your computer (on any web browser), from your cell phone (app), or even from a tablet. All you need is a stable internet connection.


From anywhere

The ubiquity of extensions means that users can connect from anywhere in the world as long as they are connected to the internet.


No extra costs, no installations

WebRTC technology does not require IP phones or installations, so you can use any device you already own.

No fixed term contracts!

Why choose Fonvirtual?


Because you don't need to buy any phones or software

With our Virtual PBX you don’t have to make any expensive IP phones purchases. Everything will go from the cloud to the device you want and wherever you want. No softphone needed.



Because you will be able to set your PBX up as you want

Let us help you achieve the perfect virtual PBX configuration for your business. We will give you the best advice and if you want to we’ll make all the changes for you.


Because we offer the best technology

Fonvirtual isn’t just the latest VoIp technology (WecRTC) it also offers all the advanced features that will make your business communications stand out.


Because we are exclusively dedicated to you

Fonvirtual is specialized in Virtual PBX. Who else can say that? Our technicians will know how to help and assist you so you can enjoy the most personalized virtual telecom experience.



Let us solve your questions about virtual PBX

What is a virtual PBX?

A virtual PBX, otherwise known as a virtual switchboard, is a telephone system that is hosted in the cloud. It is responsible for managing internal and external calls of a company efficiently, with the help of customizable features.

What are the advantages of a virtual PBX?

Having a virtual PBX, otherwise known as a virtual switchboard, will allow you to manage your calls quickly and efficiently. It will also give your company a much more professional image in addition to saving you money on installation and equipment costs. Installation and additional equipment for a virtual phone system isn’t necessary. All you need is a stable internet connection in order to enjoy your virtual PBX services.

What will the extensions of my virtual PBX be like?

The extensions will be completely flexible and mobile. You can access your extensions from any internet connected device from any location in the world.

What happens if the Internet connection is cut off?

In the event of an Internet outage, Fonvirtual offers a backup plan to divert calls to other specific lines so that no calls are missed during the outage.

Can I adapt my virtual PBX to my future needs?

Yes. Because everything is hosted in the cloud, you can adjust your features, extensions, and settings at any moment

Can I modify the configuration setting of my virtual PBX?

Yes. Even if you decide on one thing in the begging, businesses often change over time. If theres a cetain feature, greeting, or distribution of calls that you do not like, you can fix it at any time.

What is the difference between a virtual number and a virtual PBX?

The configuration of your virtual PBX is very flexible and adaptable based on your business needs. You can modify your PBX whenever you want through the configuration panel. Simply log in with your username and password. Whenever you need to make modifications, whether its the distribution of calls, the management of schedules or any other feature, you can also contact us and one of our representatives will configure the changes for you. 

What is the difference between a virtual PBX and a call center software?

Our Call Center Software services include more features than the virtual PBX. This is because it allows us to combine the power of the WebRTC technology of our virtual PBX with other advanced services such as the ACD cloud (Automatic Call Distributor). The ACD cloud is responsible for distributing phone calls to the most skilled agent that is available based on the callers needs. The ACD cloud works in real-time and allocates calls efficiently. For this reason, call center software is used more frequently in customer service and companies dedicated to managing a large volume of calls in need of a more sophisticated service.

Is virtual PBX better than the traditional PBX or PSTN phone system?

Besides being less expensive than traditional phone systems, a virtual PBX also does not need any type of installations or extra equipment. Traditional switchboards, PBX or PSTN phone systems require wiring and physical equipment, hindering the mobility and flexibility of your communication system. On the other hand, with a virtual PBX, otherwise known as a virtual switchboard, you can also modify the features. You can use virtual PBX phone systems from any location, offering complete mobility and adaptability for your business.

What is the difference between an IP PBX and a WebRTC?

WebRTC is an open-source tool developed by Google that allows users to communicate through the Internet from a web browser without needing softphones, software downloads or any installations. This offers complete flexibility for your business because you can access your phone network from any web browser. On the other hand, VoIP ( despite being able to transfer voice over the Internet), cannot be used unless you have a softphone application downloaded and installed, or have accounts with physical VoIP telephones.

How much data do calls consume over the Internet?

Almost nothing. 1,000 minutes of calls will not consume more than 1GB. Calls done over WiFi can use up to 1MB of bandwidth for every 1 minute of a call.

Which browsers are compatible?

Google Chrome, Mozilla Firefox (and applications through Android and iOS devices)

How can I receive calls from my virtual PBX?

Once you have logged into your virtual PBX account with your user and password, you can receive calls from any device by connecting to the Internet, either from a web browser on your computer, your cell phone or your tablet.

Can I make calls from the business virtual PBX phone system?

With the virtual PBX you can make calls from any extension showing the company’s slogan from any device connected to the internet: Computer (browser or desktop app), mobile (app) or even a tablet. Make and receive calls from anywhere in the world. The call will appear as a regular phone call as well.

How can I transfer calls between my extensions?

It’s easy. Just dial the “#” key, followed by the extension number of the agent you want to transfer the call to. You can also speak with the agent before transferring the call to inform them of who is calling check to see if they are available, etc.

Can I record the calls from the virtual PBX phone system?

Yes. You can record your calls in real-time. This feature comes in handy because you can resume thee conversation at any time. Your calls are recorded so that you may review the conversations later.

What are the features of the virtual PBX?

Fonvirtual offers all the features so you can enjoy the most complete virtual PBX service possible.

Some of them include:

Greetings: These customized greetings may include Welcome, Busy, Out of Office Hours , etc.
For example: “Welcome to ….”, “You are speaking to …”

Options Menu: Customize your menu options based on what may interest your callers.
For example: “If you would like to speak with the Human Resources Department, press 1. To speak with the Accounting apartment, press 2. For more options, please wait on hold to speak to a service representative”. “If you would like to contact the Madrid office, press 1. To contact the Barcelona office, press 2.”

Waiting lines with music: Choose what kind of music your callers may listen to while they are on hold, plus other information.
For example: Music + “All our operators are busy at the moment. We will attend to you shortly”.

Call Recording: This is useful for managing orders or managing the quality of your customer service.

Call Transfers: Customize who you may transfer calls to and inform them that an incoming call will be transferred.

Internal Calls: Among the different extensions in your business, you can call any internal staff member easily.

Call Statistics: You can analyze your calls through many different reports. You can find information like the amount of calls answered, calls not answered, saturated calls, lost calls, and more.

Caller ID: allows you to know in which department or in what number the call originated.

Voice Mail for moments in which you are unable to answer the call.

Schedules: You can change your configuration settings to inform callers of your office hours, holidays, hours of operations during holidays, or other different occasions.

Can I use a virtual PBX from home?

As long as you have a stable internet connection, yes. You can use a virtual PBX from home by using a special app or web browser to access your PBX. Our favorite browsers are Chrome and Mozilla Firefox.

Can I use PBX for customer service?

Yes. The virtual PBX is perfect for customer service. The management of calls, the assignment of agents based on the needs of the client, and the easy access to the virtual PBX allows us to offer an efficient and optimized customer service. Thanks to all of its features, such as menu options, main greetings, etc., your business will now present itself with a much more professional image to your customers.

Can I use a virtual PBX system for small business?

Yes, in fact it is a great opportunity for small businesses. Our virtual PBX does not require purchasing new equipment or hardware and does not have any service or installation fees. Small business employees can make and receive calls from their own phones or computers. A virtual PBX phone networking system is ideal for small businesses due to the flexibility it provides. In addition, the additional features of the PBX (greetings, options menu, schedules, etc.) will give your company a more professional and established image, despite the size of your business.

Can I use a virtual PBX for Universities?

Of course! The virtual PBX is perfect for managing the volume of calls that Universities handle each day. Workers can receive and make calls from the University’s main phone number from any compute they already use at work. What if they want to use their cell phone instead? They can do that as well!
The additional features of the virtual PBX give a much more professional image to the University,such as having an options menu that directs callers to the department they are looking for in the most efficient way possible. But they can also set schedules, waiting queues with music for whenever a caller is on hold, voice mailbox, etc.

Is virtual PBX cheaper than a traditional landline phone system?

Yes. Landline phones, otherwise known as traditional PSTN phone systems, require expensive equipment, installation fees and maintenance costs. A virtual PBX, however, is accessible from anywhere and does not require specific equipment for it to function. With any device that connects to the Internet, you can make and receive calls from the virtual PBX.

Does a hosted PBX cost more?

Yes. Hosted PBX has higher maintenance fees than a virtual PBX. A virtual PBX is better for remote teams, as well. You also don’t need any physical IP phones.

How does a virtual PBX work?

A virtual PBX (Private Branch Exchange) is a phone networking system that uses IP communications, or VoIP, to make and receive calls through the internet. Because of this, you can now make business calls from absolutely any location, as long as you are connected to the internet. Calls are made through a secure server instead of a PSTN (Public Switched Telephone Network). You can also use any device, such as a laptop or smartphone instead of physical landline phones to make and receive calls.

Self-manageable: Your virtual PBX is completely self manageable. If there’s any configuration changes you want to make, you can change it through your virtual PBX. Any adjustments or personalization features can all be managed by your business.

Flexibility: Whether your business is shrinking or expanding, your virtual PBX will adapt to your business needs. You can choose as many extensions or phone numbers as you need, and won’t need to pay extra for any services you do not use. If you need more features, Fonvirtual can provide them for you.

Transparency: Along with having the best business communication tool known as a virtual PBX, you will also receive statistical data for all of your calls, messages and video conferences. Thanks to statistics, you will be able to view everything through a set of reports. You can view which calls are answered, which calls are dropped, which agent picks up each call, the time and duration of the call, and so much more. With virtual PBX, there is complete transparency your performance.

Mobility: No matter where you are located, you can make and receive calls as long as you have internet. Because of this, customers can also reach you easily from any location. Your agents can be spread across different time zones if need be to provide 4 hour service. Or, you can use international phone numbers to show an area code from different countries, even if your agents are all in one place. With the amount of mobility virtual PBX services offer, you will no longer need to be tied to one desk in order to take important phone calls.

Integration: Virtual PBX can be integrated with your CRM tools. You can integrate any CRM tool that your business may already use with virtual PBX to analyze all of the call information you need. Because of this, you can make the most of your caller information and see what works best and what needs work based on your customer service.

How do I set up a virtual PBX?

1. To first set up your virtual PBX, contact Fonvirtual at our Contact Us page. We will discuss with you what exactly you are looking for so we can set up a virtual PBX business solution that would work best for you.

2. Set up your virtual and/or international phone numbers. You can choose as many different phone numbers and extensions as you would like, depending on your business needs.

3. Customize your features. Set up which phones you would like to ring, create group functions, customizable options menus, etc. Virtual PBX systems are very flexible and can adapt to your business needs. You can self-manage all of your features whether you decide to expand or shrink your company later on.

Does VoIP PBX slow down the internet?

Somewhat. However, VoIP PBX calls actually use less internet bandwidth than surfing the web. However, we can check with you beforehand and make sure your internet speed is compatible with our services. Depending on how many calls are happening at once using the same WiFi network, we would suggest increasing your speed if you commonly take over 5 calls at the same time using the same network.

Can VoIP be tapped?

Because your voice is encrypted every time you make a call, it is completely useless to hackers. Even if you decide to take a call using an insecure WiFi network, there is no actual sound that passes through the internet since your voice is being digitized when it is being transmitted. With traditional PSTN phone systems, calls could easily be tapped. VoIP makes this impossible. Luckily, your virtual PBX uses VoIP so that your calls are much more secure. 

What does PBX mean?

PBX stands for Private Branch Exchange. A PBX is a private telephone networking system that is used in any business or company. Fonvirtual makes PBX completely virtual, which allows call customization, automation, transparency, and mobility. 

What is a virtual PBX VoIP?

A virtual PBX VoIP (Private Branch Exchange, Voice over Internet Protocol), is a business phone networking system where users are able to make and receive calls entirely online. This is possible by accessing your service either from a web browser or phone app. 

What is a virtual phone system?

A virtual phone system uses virtual internet phone lines to make and receive calls, messages, and other features. It works the same way as a regular landline or cell phone, however, you can also customize the location of your phone number, as well as menu options when someone makes a call to your number. 

What is the difference between PBX and PABX?

PBX (Private Branch Exchange) and PABX (Private Automatic Branch Exchange) commonly refer to the same thing. Phone operators once had to manually wire phone calls to the corresponding place in order to transfer calls. This was known as PBX. Once this could be done without humans and the process was automated, this was called PABX. However, a virtual PBX today is automated and requires no human interaction to transfer calls to the correct location at all. Video conferencing is also a possibility thanks to virtual PBX. 

What is PSTN and PBX?

PSTN is a Public Switched Telephone Network. This is a type of technology used by traditional PBS systems that require analog phones to make and receive calls.