Voice

Build next-generation calling applications with integrated AI, plug-and-play compatibility with other providers, and infinite scalability

Whether building a UCaaS solution, modernizing a legacy IVR, augmenting CX with AI, or migrating from another provider's APIs, our comprehensive technical references and guides have you covered.

Try it out

SWML

SWML

version: 1.0.0
sections:
  main:
    - record_call:
        format: mp3
        direction: "both"

cXML

cXML

<?xml version="1.0" encoding="UTF-8"?>
  <Response>
    <Record/>
  </Response>

Relay Realtime SDK (Server)

Relay Realtime SDK (Server)

import { SignalWire } from "@signalwire/realtime-api";

const client = await SignalWire({ project: "PROJECT_ID", token: "AUTH_TOKEN" })

const voiceClient = client.voice;

// Setup a voice client to listen for incoming calls
await voiceClient.listen({
  topics: ['office'],
  onCallReceived: async (call) => {
    // Answer the call
    call.answer();

    // Record the call
    call.recordAudio({
      format: "mp3",
      direction: "both"
    });
  }
});

Call Flow Builder

Call Flow Builder

📚 Call Flow Builder docs

SWML

SWML

version: 1.0.0
sections:
  main:
    - connect:
        from: "%{call.from}"
        to: "+1XXXXXXXXXX"

Relay Realtime SDK (Server)

Relay Realtime SDK (Server)

import { SignalWire, Voice} from "@signalwire/realtime-api";

const client = await SignalWire({ project: "ProjectID Here", token: "Token Here" })

const voiceClient = client.voice;

await voiceClient.listen({
  topics: ["office"],
  onCallReceived: async (call) => {

    // Answer the call
    call.answer();
    // Connect the call to the device builder plan
    let peer = await call.connectPhone({
      // Replace the to parameter with a valid phone number
      to: "+1XXXXXXXXXX",
      from: call.from
    });

    // wait for peer to hangup
    await peer.disconnected();
    // hangup the call
    call.hangup();
  }
});

Call Flow Builder

Call Flow Builder

📚 Call Flow Builder docs

cXML

cXML

<?xml version="1.0" encoding="UTF-8"?>
<Response>
    <Dial callerId="{{From}}">+1XXXXXXXXXX</Dial>
</Response>

Relay Realtime SDK (Server)

Relay Realtime SDK (Server)

import { SignalWire } from "@signalwire/realtime-api";

const client = await SignalWire({ project: "ProjectID Here", token: "Token Here" })

const voiceClient = client.voice;

try {
  // Outbound Dial
  const call = await voiceClient.dialPhone({
    from: "+1XXXXXXXXXX",
    to: "+1YYYYYYYYY",
    timeout: 30
  });

  // Answering machine detection
  await call.detectAnsweringMachine({
    waitForBeep: true,
    endSilenceTimeout: 4,
    listen: {
      onEnded: async (event) => {
        console.log("Answering machine detection ended:", event.result);
        }
      }
    });
} catch (e) {
  console.log("Call not answered.", e);
}

REST

REST

curl https://example.signalwire.com/api/laml/2010-04-01/Accounts/{AccountSid}/Calls.json \
  -X POST \
  --data-urlencode "Url=http://your-application.com/docs/voice.xml" \
  --data-urlencode "To=+1YYYYYYYYY" \
  --data-urlencode "From=+1XXXXXXXXXX" \
  --data-urlencode "MachineDetection=DetectMessageEnd" \
  --data-urlencode "MachineDetectionTimeout=45" \
  --data-urlencode "AsyncAmd=true" \
  --data-urlencode "AsyncAmdStatusCallback=https://your-api-endpoint.com/path" \
  --data-urlencode "AsyncAmdStatusCallbackMethod=POST" \
  -u "YourProjectID:YourAuthToken"

SWML

SWML

version: 1.0.0
sections:
  main:
    - answer: {}
    - play:
        urls:
          - >-
            say:Thank you for calling SignalWire! 
            Please listen closely to the options in order to direct your call.
    - prompt:
        play: >-
            say:Press 1 to talk to sales, Press 2 to talk to Support, Press 3 to
            talk to a Customer Representative
        say_language: en-US
        max_digits: 1
        speech_hints:
          - one
          - two
          - three
    - switch:
        variable: prompt_value
        case:
          '1':
            - execute:
                dest: sales
          '2':
            - execute:
                dest: support
          '3':
            - execute:
                dest: customer
          one:
            - execute:
                dest: sales
          two:
            - execute:
                dest: support
          three:
            - execute:
                dest: customer
        default:
          - execute:
              dest: sales
  sales:
    - play:
        url: 'say:You have reached sales'
    - connect:
        to: +1XXXXXXXXXX
  support:
    - play:
        url: 'say:You have reached support'
    - connect:
        to: +1YYYYYYYYYY
  customer:
    - play:
        url: 'say:You have reached a Customer representative'
    - connect:
        to: +1ZZZZZZZZZZ

cXML

cXML

<?xml version="1.0" encoding="UTF-8"?>
  <Response>
    <Say>
      Thank you for calling SignalWire! 
      Please listen closely to the options in order to direct your call.
    </Say>
    <!-- The action attribute is the URL of the webhook that will be called when the user presses a key. -->
    <Gather action="https://example.com/IVR" input="dtmf" method="GET" timeout="3">
      <Say>If you'd like to connect to our Sales team, press 1</Say>
      <Say>If you'd like to connect to our Support Engineering Team, press 2</Say>
      <Say>If you'd like to connect to our Customer Representative, press 3</Say>
    </Gather>
  </Response>

Relay Realtime SDK (Server)

Relay Realtime SDK (Server)

import { SignalWire } from "@signalwire/realtime-api";

const client = await SignalWire({ project: "b08dacad-2f6c-4de1-93d6-cc732e0c69c5", token: "PT16d2254f1cf1be0766881a2043afe8ef9e2fc8e8f739750b" })

const voiceClient = client.voice;

// Setup a voice client to listen for incoming calls
await voiceClient.listen({
  topics: ['office'],
  onCallReceived: async (call) => {
    // Answer the call
    call.answer();

    await call.playTTS({
      text: "Thank you for calling SignalWire! Please listen closely to the options in order to direct your call.",
    });

    await handlePromptTTS(call);
  }
})

async function handlePromptTTS(call) {
  await call.promptTTS({
    
    text: "Press 1 to talk to sales, Press 2 to talk to Support, Press 3 to talk to a Customer Representative",
    digits: {
      max: 1,
      digitTimeout: 5,
    },
    listen: {
      onEnded: async (prompt) => {
        const digits = prompt.digits;

        if (digits === "1") {
          await connectCall(call, "sales", "+1XXXXXXXXXX");
        }

        else if (digits === "2") {
          await connectCall(call, "support", "+1YYYYYYYYY");
        }

        else if (digits === "3") {
          await connectCall(call, "a customer representative", "+1ZZZZZZZZZZ");
        }
        else {
          await call.playTTS({
            text: "Invalid option. Please try again.",
          });

          handlePromptTTS(call);
        }
      }
    }
  });
}

async function connectCall(call, destination, toNumber) {
  await call.playTTS({
    text: `Connecting you to ${destination}`,
  });

  let peer = await call.connectPhone({
    from: call.from,
    to: toNumber,
    timeout: 30
  });

  await peer.disconnected();
  call.hangup();
}

Call Flow Builder

Call Flow Builder

📚 Call Flow Builder docs

SWML

SWML

version: 1.0.0
sections:
  main:
    - record_call:
        format: mp3
        direction: "both"

cXML

cXML

<?xml version="1.0" encoding="UTF-8"?>
  <Response>
    <Record/>
  </Response>

Relay Realtime SDK (Server)

Relay Realtime SDK (Server)

import { SignalWire } from "@signalwire/realtime-api";

const client = await SignalWire({ project: "PROJECT_ID", token: "AUTH_TOKEN" })

const voiceClient = client.voice;

// Setup a voice client to listen for incoming calls
await voiceClient.listen({
  topics: ['office'],
  onCallReceived: async (call) => {
    // Answer the call
    call.answer();

    // Record the call
    call.recordAudio({
      format: "mp3",
      direction: "both"
    });
  }
});

Call Flow Builder

Call Flow Builder

📚 Call Flow Builder docs

SWML

SWML

version: 1.0.0
sections:
  main:
    - connect:
        from: "%{call.from}"
        to: "+1XXXXXXXXXX"

Relay Realtime SDK (Server)

Relay Realtime SDK (Server)

import { SignalWire, Voice} from "@signalwire/realtime-api";

const client = await SignalWire({ project: "ProjectID Here", token: "Token Here" })

const voiceClient = client.voice;

await voiceClient.listen({
  topics: ["office"],
  onCallReceived: async (call) => {

    // Answer the call
    call.answer();
    // Connect the call to the device builder plan
    let peer = await call.connectPhone({
      // Replace the to parameter with a valid phone number
      to: "+1XXXXXXXXXX",
      from: call.from
    });

    // wait for peer to hangup
    await peer.disconnected();
    // hangup the call
    call.hangup();
  }
});

Call Flow Builder

Call Flow Builder

📚 Call Flow Builder docs

cXML

cXML

<?xml version="1.0" encoding="UTF-8"?>
<Response>
    <Dial callerId="{{From}}">+1XXXXXXXXXX</Dial>
</Response>

Relay Realtime SDK (Server)

Relay Realtime SDK (Server)

import { SignalWire } from "@signalwire/realtime-api";

const client = await SignalWire({ project: "ProjectID Here", token: "Token Here" })

const voiceClient = client.voice;

try {
  // Outbound Dial
  const call = await voiceClient.dialPhone({
    from: "+1XXXXXXXXXX",
    to: "+1YYYYYYYYY",
    timeout: 30
  });

  // Answering machine detection
  await call.detectAnsweringMachine({
    waitForBeep: true,
    endSilenceTimeout: 4,
    listen: {
      onEnded: async (event) => {
        console.log("Answering machine detection ended:", event.result);
        }
      }
    });
} catch (e) {
  console.log("Call not answered.", e);
}

REST

REST

curl https://example.signalwire.com/api/laml/2010-04-01/Accounts/{AccountSid}/Calls.json \
  -X POST \
  --data-urlencode "Url=http://your-application.com/docs/voice.xml" \
  --data-urlencode "To=+1YYYYYYYYY" \
  --data-urlencode "From=+1XXXXXXXXXX" \
  --data-urlencode "MachineDetection=DetectMessageEnd" \
  --data-urlencode "MachineDetectionTimeout=45" \
  --data-urlencode "AsyncAmd=true" \
  --data-urlencode "AsyncAmdStatusCallback=https://your-api-endpoint.com/path" \
  --data-urlencode "AsyncAmdStatusCallbackMethod=POST" \
  -u "YourProjectID:YourAuthToken"

SWML

SWML

version: 1.0.0
sections:
  main:
    - answer: {}
    - play:
        urls:
          - >-
            say:Thank you for calling SignalWire! 
            Please listen closely to the options in order to direct your call.
    - prompt:
        play: >-
            say:Press 1 to talk to sales, Press 2 to talk to Support, Press 3 to
            talk to a Customer Representative
        say_language: en-US
        max_digits: 1
        speech_hints:
          - one
          - two
          - three
    - switch:
        variable: prompt_value
        case:
          '1':
            - execute:
                dest: sales
          '2':
            - execute:
                dest: support
          '3':
            - execute:
                dest: customer
          one:
            - execute:
                dest: sales
          two:
            - execute:
                dest: support
          three:
            - execute:
                dest: customer
        default:
          - execute:
              dest: sales
  sales:
    - play:
        url: 'say:You have reached sales'
    - connect:
        to: +1XXXXXXXXXX
  support:
    - play:
        url: 'say:You have reached support'
    - connect:
        to: +1YYYYYYYYYY
  customer:
    - play:
        url: 'say:You have reached a Customer representative'
    - connect:
        to: +1ZZZZZZZZZZ

cXML

cXML

<?xml version="1.0" encoding="UTF-8"?>
  <Response>
    <Say>
      Thank you for calling SignalWire! 
      Please listen closely to the options in order to direct your call.
    </Say>
    <!-- The action attribute is the URL of the webhook that will be called when the user presses a key. -->
    <Gather action="https://example.com/IVR" input="dtmf" method="GET" timeout="3">
      <Say>If you'd like to connect to our Sales team, press 1</Say>
      <Say>If you'd like to connect to our Support Engineering Team, press 2</Say>
      <Say>If you'd like to connect to our Customer Representative, press 3</Say>
    </Gather>
  </Response>

Relay Realtime SDK (Server)

Relay Realtime SDK (Server)

import { SignalWire } from "@signalwire/realtime-api";

const client = await SignalWire({ project: "b08dacad-2f6c-4de1-93d6-cc732e0c69c5", token: "PT16d2254f1cf1be0766881a2043afe8ef9e2fc8e8f739750b" })

const voiceClient = client.voice;

// Setup a voice client to listen for incoming calls
await voiceClient.listen({
  topics: ['office'],
  onCallReceived: async (call) => {
    // Answer the call
    call.answer();

    await call.playTTS({
      text: "Thank you for calling SignalWire! Please listen closely to the options in order to direct your call.",
    });

    await handlePromptTTS(call);
  }
})

async function handlePromptTTS(call) {
  await call.promptTTS({
    
    text: "Press 1 to talk to sales, Press 2 to talk to Support, Press 3 to talk to a Customer Representative",
    digits: {
      max: 1,
      digitTimeout: 5,
    },
    listen: {
      onEnded: async (prompt) => {
        const digits = prompt.digits;

        if (digits === "1") {
          await connectCall(call, "sales", "+1XXXXXXXXXX");
        }

        else if (digits === "2") {
          await connectCall(call, "support", "+1YYYYYYYYY");
        }

        else if (digits === "3") {
          await connectCall(call, "a customer representative", "+1ZZZZZZZZZZ");
        }
        else {
          await call.playTTS({
            text: "Invalid option. Please try again.",
          });

          handlePromptTTS(call);
        }
      }
    }
  });
}

async function connectCall(call, destination, toNumber) {
  await call.playTTS({
    text: `Connecting you to ${destination}`,
  });

  let peer = await call.connectPhone({
    from: call.from,
    to: toNumber,
    timeout: 30
  });

  await peer.disconnected();
  call.hangup();
}

Call Flow Builder

Call Flow Builder

📚 Call Flow Builder docs

SWML

SWML

version: 1.0.0
sections:
  main:
    - record_call:
        format: mp3
        direction: "both"

cXML

cXML

<?xml version="1.0" encoding="UTF-8"?>
  <Response>
    <Record/>
  </Response>

Relay Realtime SDK (Server)

Relay Realtime SDK (Server)

import { SignalWire } from "@signalwire/realtime-api";

const client = await SignalWire({ project: "PROJECT_ID", token: "AUTH_TOKEN" })

const voiceClient = client.voice;

// Setup a voice client to listen for incoming calls
await voiceClient.listen({
  topics: ['office'],
  onCallReceived: async (call) => {
    // Answer the call
    call.answer();

    // Record the call
    call.recordAudio({
      format: "mp3",
      direction: "both"
    });
  }
});

Call Flow Builder

Call Flow Builder

📚 Call Flow Builder docs

Get started

Buy a phone number

SignalWire phone numbers in the Dashboard

Quickstart with AI

Deploy a serverless voice AI Agent and call it over the PSTN in under 5 minutes with SWML

Make your first phone calls

The fundamentals of your first calling app

Migrate a Twilio application

Get started with our Compatibility API

No-code apps with Call Flow Builder

Create a drag-and-drop calling application

Choose an API

SignalWire's advanced APIs and elastic cloud infrastructure make it a breeze to build modern and powerful voice applications using both PSTN and SIP endpoints.

• SignalWire REST API: A robust, modern and flexible API for building integrated, advanced communications applications.
• Compatibility API: Ideal for porting code from other providers. It can run serverless, but it also supports Python, PHP, Node.js, and other languages.
• Realtime API: This API is ideal if you are an advanced developer and you want flexible, modern and realtime SDKs for Node.js.

SignalWire API

High-quality, scalable, and secure voice API

Compatibility API & cXML

Easily migrate from Twilio and other providers

RELAY Realtime Server SDK

Next-gen server telephony applications powered by our RELAY WebSocket API

RELAY Browser SDK

Bring telephone capabilities to the browser with our Node.js SDK

Low-code and no-code solutions

Call Flow Builder

Drag-and-drop, no-code call application builder

SWML

Write realtime, AI-integrated calling applications using simple JSON or YAML scripts

Popular guides

SIP trunking

Route SIP traffic through the SignalWire platform to your PBX system.

Answering machine detection

Setup AMD using our Compatibility API and Node.js.

Build an Interactive Voice Response (IVR) System

Learn how to build an IVR with Node.js.

Setting Up a SIP Endpoint

This guide will show how you can create a SIP endpoint and register it to a phone number for handling incoming calls.

Getting Started with SIP

Guides that focus on the basic setup for SIP calling.