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How it works

How browser calling works, from WebRTC in your tab to a ringing phone

By · Updated · 17 min read

TL;DR

A browser call runs on WebRTC, a set of open standards built into all major browsers[1]: once you allow the microphone[2], the page compresses your voice and sends it encrypted to the calling service[3]. Between two users of the same app the call stays on the internet, which is how WhatsApp Web calls can be free[4]. To ring a landline or mobile, the service's gateway turns the call into an ordinary phone call[5], and the network that owns the number charges per minute to deliver it[6]: that last hop is what you pay for.

Key facts

What is WebRTC?

WebRTC (Web Real-Time Communication) is the calling engine inside your browser: a JavaScript API plus a suite of communication protocols that lets a web page send live audio and video without a plug-in or a separate app[7]. The W3C and the IETF made it an official standard on 26 January 2021[7], and all major browsers ship it[1].

The open-source WebRTC project is backed by Apple, Google, Microsoft and Mozilla[1], the companies behind Safari, Chrome, Edge and Firefox, so one dialer page can work in all four. Browsers include it royalty-free[7], so the technology itself carries no licence fee for you or for the calling service.

I read the standards behind a browser call to see which parts matter when you dial a phone number. Five do:

The parts of WebRTC a phone call uses
PartWhat it doesWhat you notice
Microphone access (getUserMedia)Gives the page your microphone, only on an HTTPS page and only after you allow it[2]The permission prompt; Chrome lets you allow a site while you visit, this time only, or never[11]
Codecs (Opus and G.711)Compress your voice; every browser must support both[8]Usually nothing: Opus scales from 6 kbit/s narrowband speech up to 510 kbit/s[12]
Encryption (DTLS-SRTP)Encrypts the audio on every WebRTC connection: DTLS-SRTP must be offered for every media channel, and unencrypted audio is not allowed[3]Nothing to switch on, and nothing to switch off
Connection set-up (ICE, STUN, TURN)Finds a path through routers and firewalls, and relays the audio through a server when a direct path is blocked[13]Usually nothing; on networks that block direct connections, the audio takes the relay
Keypad tones (telephone-event)Sends the digits 0 to 9, * and # as separate events that every endpoint must handle[8]Phone menus that say 'press 1' react to the page's dial pad

From the IETF and W3C standards and MDN, read .

Browser dialers that call phone numbers name WebRTC in their own documentation: PopTox[14], Globfone[15], TwinPhone[16], Call2Friends[17] and Zadarma's webphone[18] all say they are built on it.

How does a browser call reach a landline or mobile?

Through a gateway. The page captures your voice, WebRTC carries it encrypted to the calling service, and the service's gateway turns it into an ordinary phone call that a carrier delivers to the number you dialled. As the FCC puts it, a call to a regular number is converted to a regular telephone signal before it reaches the destination[5].

How a browser call reaches a phoneYour browser sends audio over WebRTC to the service, a gateway converts it to a regular phone call, and the phone network rings the number you dialled.encrypted audioSIPPSTNringsYour browserService (WebRTC)SIP gatewayPhone networkTheir phoneHow a browser call reaches a phoneYour browser sends audio over WebRTC to the service, a gateway converts it to a regular phone call, and the phone network rings the number you dialled.encrypted audioSIPPSTNringsYour browserService (WebRTC)SIP gatewayPhone networkTheir phone
Five stops on the way to a phone: your tab, WebRTC, the provider's gateway, the phone network and the handset.

What happens between pressing Call and hearing the ring, step by step:

  1. The dialer page loads over HTTPS. On an unencrypted page the browser does not offer the microphone at all[2].
  2. You allow the microphone. Chrome asks per site, and a site you block cannot run a call[11].
  3. The page signals the call. It sends the number you typed to the provider. WebRTC leaves this step to each service[19]; one standard option is SIP carried over a WebSocket[20].
  4. Your voice travels to the provider. The browser compresses it, with Opus as the preferred codec[8], and encrypts it with SRTP[3]. If a router blocks a direct path, a relay server passes the audio on[13].
  5. The gateway crosses into the phone network. The provider turns the stream into a regular telephone signal[5], using G.711 where needed, the codec WebRTC shares with legacy phone systems[8], and hands the call to a phone carrier.
  6. The network that owns the number rings the phone. It charges the caller's side for delivering, or terminating, the call[6], and the person you call needs nothing more than an ordinary phone[5].

When the call lands on a phone menu, your key presses get through as well, because every WebRTC endpoint must be able to send keypad digits as separate tone events[8]. The half of the journey after the gateway, from carrier to handset, is covered in what the PSTN is and how it routes a call.

What is the difference between WebRTC and SIP?

WebRTC carries the audio; SIP sets up the call. WebRTC deliberately leaves call set-up, the signalling, to each service[19]. SIP, the Session Initiation Protocol, is the IETF's signalling standard for creating, changing and ending sessions such as internet telephone calls[21]. A browser phone can use both: WebRTC in the tab, SIP towards the phone side.

WebRTC and SIP side by side
QuestionWebRTCSIP
What does it do?Captures and sends the audio, and finds a network path[13]Sets up, changes and ends calls[21]
Where does it run?Inside the browser, with nothing to install[22]In softphone apps and on provider and office phone systems (PBXs)[23]; in a web page, over a WebSocket[20]
Is the audio encrypted?Always: media must use SRTP[3]Optional: Zadarma's set-up guide, for one, lists SRTP as a setting to turn on[24]
What do you sign in with?The website's own accountA SIP account, which a generic app can take from any SIP provider[23]

From RFC 3261, RFC 7118, RFC 8827, MDN and provider documentation, read .

None of the consumer web dialers I read says which signalling its dial pad uses, so I can't tell you which of them run on SIP. Business platforms are more open: Google Voice's SIP Link plugs an organisation's existing carrier contract and equipment into Google Voice[25], and Zadarma offers both a WebRTC webphone[18] and guides for connecting office phone systems over SIP[24].

A softphone is the installed cousin of a browser phone: it signs in with a SIP account instead of a website login. Softphones and browser phones compared covers which suits whom.

Why are app-to-app calls free while calls to phone numbers cost money?

Because only a call to a number uses another company's network. A WhatsApp Web call runs between two internet users, so it costs you nothing[4]. A call to a landline or mobile must be handed to the operator that owns that number, and operators charge each other per minute to deliver, or terminate, calls on their networks[6].

The FCC draws the same line between VoIP services that reach only people on the same service and those that can call anyone with a telephone number[5]. Free app-to-app calling is the first kind; a web dialer is the second, and it pays the phone networks for every connected minute.

Termination charges depend on the network you reach. In the EU they are capped at $0.002 a minute for mobiles and $0.001 for landlines[6][6], but the caps do not cover calls from numbers outside the EU[6]. Retail rate cards show the same split: Yolla charges $0.06 a minute to UK landlines and $0.10 to UK mobiles[9], and Quo says its rates vary by carrier within each country[26].

Each service's own model sits on top. From the US, almost all Google Voice calls to US and Canadian numbers are free[27], but personal accounts are available only in the US[28]. TwinPhone has no free tier[29], needs a top-up of at least $10 before the first call[30], and charges $0.12 a minute to UK mobiles[10], more than Yolla.

How five services handle reach, free use, incoming calls and encryption, as published on :

Comparison
ServiceCalls phone numbersFree optionIncoming calls and caller IDPrivacy
WhatsAppWhatsApp contacts and link guests only[31]Yes, no time limit[4]Calls from WhatsApp users ring in the tab[31]End-to-end encrypted[32]
TwinPhoneLandlines and mobiles, 145+ countries[16]No: paid credit only, no trial[29]With a rented US/Canada number, $0.02/min[33]Encrypted in transit, not end-to-end[34]
Google VoiceUS, Canadian and international numbers[27]Yes, personal plan, calling from the US[35]Yes: your free number rings in the tab[36]No end-to-end claim; Google stores call data[37]
YollaMobiles and landlines worldwide[38]No; free Yolla-to-Yolla calls only in the app[38]No: outbound only[38]Encrypted connection; no end-to-end claim[38]
PopToxMobiles and landlines; 246 countries claimed[39]Yes: same number up to 5 times a day[40]None found; shared caller ID 218-414-1141[41]Site and 2016 terms conflict on encryption[42]

On a phone, scroll the table sideways to see every column.

The free options and their catches are in free browser calls between apps, per-minute prices by destination in rates by country, and every service I scored in my full comparison of browser calling services.

How does VoIP work, and is a browser call VoIP?

Yes, a browser call is VoIP with the browser as the phone. VoIP turns your voice into a digital signal that travels over the internet, and a call to a regular number is converted to a regular telephone signal before it arrives[5]. VoIP products differ mainly in the device: a computer, a VoIP desk phone or an ordinary phone on an adapter[5], and now a browser tab.

Ways to place an internet call, and where a browser fits
Way to callWhat you installWhat you sign in withCalls phone numbers?
Web dialer (Yolla Web, TwinPhone, PopTox)Nothing: the page uses the browser's WebRTC[16]An account on the site, or none for PopTox's free calls[43]Yes, through the provider's gateway[34]
Messenger in a tab (WhatsApp Web, Google Meet)Nothing[4]Your messenger or Google accountWhatsApp: only WhatsApp contacts and call-link guests[31][44]; Meet: only in Workspace meetings[45]
Softphone app (MicroSIP)An app on the computerA SIP account from any provider[23]If the SIP provider sells calls to numbers
VoIP desk phone or adapterA device on your broadband line[5]The provider's accountDepends on the plan[5]
Carrier Wi-Fi CallingNothing; it is part of your mobile line[46]Your SIM and carrier planYes: your normal calls go over Wi-Fi instead of the cellular network[47]

From the FCC, carrier and provider pages, read .

Two lookalikes are not browser calling at all. Carrier Wi-Fi Calling is a feature of your mobile plan that works only if your carrier offers it[46], and Microsoft Phone Link makes calls through your own linked phone, with Bluetooth on both devices[48]. Wi-Fi Calling versus a browser call explains when each makes sense.

VoIP in general has known weak spots: some services stop working in a power cut[5], and not all connect directly to 911[5]. VoIP against a landline at home weighs those trade-offs for a household line.

What changes when a call leaves the internet?

Encryption, caller ID and what you can dial all change at the gateway. WebRTC encrypts the audio from your browser to the provider[3], but past the gateway it travels as an ordinary phone call, so a call to a number is never end-to-end encrypted. App-to-app calls never reach a gateway, which is how WhatsApp can encrypt them end to end[32].

An app-to-app call versus a call to a phone number
QuestionApp-to-app call (WhatsApp Web, Meet)Call to a number (web dialer)
Who can you reach?People on the same app, or guests who open a call link[44]Landlines and mobiles in the countries the provider connects[5]
What does it cost?Nothing on WhatsApp Web[4]Per minute, for example $0.02 to the US on TwinPhone[10]
Is it end-to-end encrypted?Yes on WhatsApp[32]; opt-in for Meet calls between personal accounts[49]No: encrypted to the provider, then the carrier's own security applies[34]
What does the other person see?Your account on that appThe number the service sends: one shared number on PopTox[41], your own number on Yolla, its homepage says[50], a shared, rented or verified number on TwinPhone[16]
Can you dial emergency numbers?Not on WhatsApp[51]Not on TwinPhone[29] or free Google Voice[27]
Does the other person need internet?Yes, and the same appNo, an ordinary phone is enough[5]

Checked .

TwinPhone, which sponsors this site, describes the same bridge in its explainer on browser-based calling: the browser leg is encrypted, then connected to the public phone network, where the recipient carrier's security model applies[34]. PopTox's homepage, by contrast, advertises end-to-end WebRTC encryption[39], which a call that ends on a phone line cannot have.

Caller ID, emergency calling and the IP addresses WebRTC can reveal[52] are safety questions; my privacy and safety checks answer them service by service.

In this guide

Frequently asked questions

Is WebRTC free to use?

Yes. Browsers include WebRTC as a royalty-free feature[7], and the reference project is open source, backed by Apple, Google, Microsoft and Mozilla[1]. Nobody pays to use it inside a tab. What costs money is reaching a phone number, because the network that owns the number charges for delivering the call[6]. That is why web dialers bill per minute while app-to-app calls are free.

Is a WebRTC call peer-to-peer?

It can be. WebRTC lets two browsers exchange audio directly, peer to peer, without plug-ins[22], but when a router or firewall blocks the direct path, a TURN server relays the audio instead[13]. A call to a phone number is never peer to peer: your browser connects to the provider, whose gateway converts the stream into a regular telephone signal before it reaches the number you dialled[5].

Which websites and apps use WebRTC for calls?

Most services that call from a tab. Web dialers such as PopTox and TwinPhone say so in their documentation[14][16], as do business phone systems such as Ringover[53] and JustCall[54]. Telegram's open-source web client switches calls on only where the browser supports WebRTC[55].

Do I need to install anything to make a browser call?

No. WebRTC is part of the browser, so calls need no plug-in or extra software[22]. You need a current browser, a microphone and an internet connection; TwinPhone, for example, names Chrome, Edge, Firefox, Brave and Safari on computers and phones[16]. The one thing you grant is microphone access, which the browser asks for site by site[11].

How much bandwidth or data does a browser call use?

Not much. For Google Voice, Google asks for at least 32 kbps per call participant and recommends more than 50 kbps for good quality[56]. At 50 kbps, an hour of audio in one direction comes to about 22 MB. Opus, the codec browsers prefer[8], can go as low as 6 kbit/s for narrowband speech[12].

Is a browser call end-to-end encrypted?

Only between users of the same app, and only when that app says so: WhatsApp encrypts its calls end to end[32]. A call to a phone number can't be, because the provider's gateway turns it into an ordinary phone call. WebRTC encrypts it from your browser to the provider[3], and TwinPhone, for one, says the final carrier leg follows the recipient carrier's security model[34].

Why does calling a mobile cost more than calling a landline?

One reason is the charge the receiving network makes for delivering the call[6]: mobile networks are allowed to charge more. In the EU the cap is $0.002 a minute for mobiles against $0.001 for landlines[6][6]. Retail rate cards show the same gap: TwinPhone lists UK landlines at $0.06 and UK mobiles at $0.12 a minute[10].

Can a browser receive phone calls?

Only if the service gives you a phone number: Google Voice rings in the browser while you are signed in with the window open[36], and a rented TwinPhone US, Canadian or Puerto Rico number rings in the tab[16] at $0.02 a minute[33]. Yolla Web is outbound only[38], and PopTox shows one shared caller ID for everyone[41]; which number your call shows, and whether it rings back, depends on the service.

Why does the browser ask for my microphone?

Because a web page gets no microphone access until you grant it, and only on a secure HTTPS page[2]. Chrome offers to allow a site while you visit, this time only, or never, and lists allowed and blocked sites in its settings[11]. On a Mac, the browser itself also needs microphone permission in System Settings[57], and on Windows, desktop apps, browsers included, need microphone access switched on[58].

Prices are converted to USD at the rate of October 30, 2026 (ExchangeRate-API (open access endpoint)). Hover over a price to see the operator's original price.

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Sources

  1. WebRTC · Google WebRTC team · checked November 1, 2026
  2. MediaDevices: getUserMedia() method - Web APIs | MDN · MDN Web Docs (Mozilla) · checked November 1, 2026
  3. RFC 8827: WebRTC Security Architecture · IETF (RFC Editor) · checked November 1, 2026
  4. Introducing Web Calling on WhatsApp, Plus More New Updates (WhatsApp Blog, July 28, 2026) · checked November 1, 2026
  5. Voice Over Internet Protocol (VoIP) | Federal Communications Commission · FCC · checked November 1, 2026
  6. The EU-wide voice-call termination rates become applicable today · European Commission · checked November 1, 2026
  7. Web Real-Time Communications (WebRTC) transforms the communications landscape; becomes a World Wide Web Consortium (W3C) Recommendation and multiple Internet Engineering Task Force (IETF) standards | W3C · W3C · checked November 1, 2026
  8. RFC 7874: WebRTC Audio Codec and Processing Requirements · IETF · checked November 1, 2026
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  10. International Calling Rates — Pay As You Go, Per Minute - TwinPhone · checked November 1, 2026
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  21. RFC 3261: SIP: Session Initiation Protocol · IETF (RFC Editor) · checked November 1, 2026
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  32. About end-to-end encryption - WhatsApp Help Center · checked November 1, 2026
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