Connect your ElevenLabs Conversational AI agent to phone calls and create human-like voice experiences using Twilio’s Voice API.

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What You’ll Need

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Agent Configuration

Before integrating with Twilio, you’ll need to configure your agent to use the correct audio format supported by Twilio.
1

Configure TTS Output

  1. Navigate to your agent settings
  2. Go to the Voice Section
  3. Select “μ-law 8000 Hz” from the dropdown
2

Set Input Format

  1. Navigate to your agent settings
  2. Go to the Advanced Section
  3. Select “μ-law 8000 Hz” for the input format

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Implementation

Looking for a complete example? Check out this Javascript implementation on GitHub.
1

Initialize the Project

First, set up a new Node.js project:
mkdir conversational-ai-twilio
cd conversational-ai-twilio
npm init -y; npm pkg set type="module";
2

Install dependencies

Next, install the required dependencies for the project.
npm install @fastify/formbody @fastify/websocket dotenv fastify ws
3

Create the project files

Create a .env & index.js file with the following code:
ELEVENLABS_AGENT_ID=<your-agent-id>
4

Run the server

You can now run the server with the following command:
node index.js
If the server starts successfully, you should see the message [Server] Listening on port 8000 (or the port you specified) in your terminal.

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Twilio Setup

1

Create a Public URL

Use ngrok to make your local server accessible:
ngrok http --url=<your-url-here> 8000
2

Configure Twilio

  1. Go to the Twilio Console
  2. Navigate to Phone Numbers → Manage → Active numbers
  3. Select your phone number
  4. Under “Voice Configuration”, set the webhook for incoming calls to: https://your-ngrok-url.ngrok.app/incoming-call-eleven
  5. Set the HTTP method to POST

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Testing

  1. Call your Twilio phone number.
  2. Start speaking - you’ll see the transcripts in the ElevenLabs console.

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Troubleshooting

If the WebSocket connection fails:
  • Verify your ngrok URL is correct in Twilio settings
  • Check that your server is running and accessible
  • Ensure your firewall isn’t blocking WebSocket connections
If there’s no audio output:
  • Confirm your ElevenLabs API key is valid
  • Verify the AGENT_ID is correct
  • Check audio format settings match Twilio’s requirements (μ-law 8kHz)

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Security Best Practices

Follow these security guidelines for production deployments:
  • Use environment variables for sensitive information
  • Implement proper authentication for your endpoints
  • Use HTTPS for all communications
  • Regularly rotate API keys
  • Monitor usage to prevent abuse