Fonoster: The open-source alternative to Twilio

Fonoster is researching an innovative Programmable Telecommunications Stack that will allow businesses to connect telephony services with the Internet entirely through a cloud-based utility.

Features

The most notable features of Fonoster are:

• [x] Multitenancy
• [x] Easy deployment of PBX functionalities
• [x] Programmable Voice Applications
• [x] NodeJS SDK
• [x] Support for Amazon Simple Storage Service (S3)
• [x] Secure API endpoints with Let's Encrypt
• [x] Authentication with OAuth2
• [X] Authentication with JWT
• [x] Role-Based Access Control (RBAC)
• [x] Plugins-based Command-line Tool
• [x] Support for Google Speech APIs

Code Examples

A Voice Application is a server that controls a call's flow. A Voice Application can use any combination of the following verbs:

• Answer - Accepts an incoming call
• Hangup - Closes the call
• Play: Takes a URL with a media file and streams the sound back to the calling party
• PlayDtmf - Takes a DTMF sequence and plays it back to the calling party
• Say - Takes a text, synthesizes the text into audio, and streams back the result
• Gather - Waits for DTMF or speech events and returns back the result
• SGather - Returns a stream for future DTMF and speech results
• Stream - Creates a bidirectional stream to send and receive audio from a caller
• Dial - Passes the call to an Agent or a Number at the PSTN
• Record - It records the voice of the calling party and saves the audio on the Storage sub-system
• Mute - It tells the channel to stop sending media, effectively muting the channel
• Unmute - It tells the channel to allow media flow

Voice Application Example:

const VoiceServer = require("@fonoster/voice").default;
const { 
  GatherSource, 
  VoiceRequest, 
  VoiceResponse 
} = require("@fonoster/voice");

new VoiceServer().listen(async (req: VoiceRequest, voice: VoiceResponse) => {
  const { ingressNumber, sessionRef, appRef } = req;

  await voice.answer();

  await voice.say("Hi there! What's your name?");

  const { speech: name } = await res.gather({
    source: GatherSource.SPEECH
  });

  await voice.say("Nice to meet you " + name + "!");

  await voice.say("Please enter your 4 digit pin.");

  const { digits } = await voice.gather({
    maxDigits: 4,
    finishOnKey: "#"
  });

  await voice.say("Your pin is " + digits);

  await voice.hangup();
});

// Your app will live at tcp://127.0.0.1:50061 
// and you can easily publish it to the Internet with:
// ngrok tcp 50061

Everything in Fonoster is an API first, and initiating a call is no exception. You can use the SDK to start a call with a few lines of code.

Example of originating a call with the SDK:

const SDK = require("@fonoster/sdk");

async function main(request) {
  const apiKey = "your-api-key";
  const apiSecret = "your-api-secret"
  const accessKeyId = "WO00000000000000000000000000000000";

  const client = new SDK.Client({ accessKeyId });
  await client.loginWithApiKey(apiKey, apiSecret);

  const calls = new SDK.Calls(client);
  const response = await calls.createCall(request);

  console.log(response); // successful response
}

const request = {
  from: "+18287854037",
  to: "+17853178070",
  appRef: "3e61ecb7-a1b6-4a93-84c3-4f1979165bca",
  // Optional metadata to be sent to the Voice Application
  metadata: {
    name: "John Doe",
    message: "Please call me back."
  }
};

main(request).catch(console.error);

Getting Started

To get started with Fonoster, use the following resources:

• Deploying Fonoster with Docker
• Guide for Early Access User
• Getting started with Fonoster
• How we created an open-source alternative to Twilio and why it matters

Give a Star! ⭐

Please give it a star if you like this project or plan to use it. Thanks 🙏

Bugs and Feedback

For bugs, questions, and discussions, please use the Github Issues

Contributing

For contributing, please see the following links:

• Contribution Documents
• Contributors

Pedro Sanders	Efrain Peralta	Angel M. Bencosme	Wandy Hernandez	Obruche Wilfred Oghenechohwo	Wardner Lara
Richard HC	Nageswari	Hoan Luu Huu	Speedy Monster	harry_dev	Kanishka Chowdhury
Brayan Munoz V.	Dede kurniawan	gabriel duncan	Prasurjya Pran Borah	Jordan	Hector Ventura
0xflotus	Manish	Osama Sehgol	Paul Sütterlin	Riad Vargas	Shailendra Paliwal
The Gitter Badger	Yuri	cdrsociate	pavan	nrjchnd	Salami Bashir
Shivam Deepak Chaudhary	Yossef Haim	telenautical	Wisdom Elendu	Judge Godwins	Jon Chin
Harish Chander	Gary Barnes	Fidal Mathew	Enmanuel Toribio	Dung Duc Huynh (Kaka)	Ciprian
Christopher Adigun	Bruno Gomes	Bruno Arueira	Antonius Ostermann	Ali Firat ARI	Alex
Albert E. Hidalgo Taveras

Sponsors

We're glad to be supported by respected companies and individuals from several industries.

Find all our supporters here

Become a Github Sponsor

Authors

• Pedro Sanders

License

Copyright (C) 2025 by Fonoster Inc. MIT License (see LICENSE for details).