ElevenLabs + Twilio: Building Voice Call Applications

Why Voice AI Is the Next Big Thing

Voice interfaces are no longer a novelty—they’re becoming the primary way people interact with software. From smart assistants to automated customer support, the demand for high‑quality, natural‑sounding text‑to‑speech (TTS) has exploded. If you’re building a voice‑first product, you’ll want to combine a reliable telephony platform with a cutting‑edge TTS engine. That’s where Twilio and ElevenLabs meet.

The Twilio Advantage

Twilio’s Programmable Voice API lets you place outbound calls, receive inbound calls, and even transcribe speech—all with a few REST calls. It abstracts away the complexities of SIP, codecs, and network provisioning, so you can focus on the user experience.

Key Twilio features for voice apps:

• Programmable Call Control – Start, hang up, mute, and play audio on the fly.
• Webhooks – Respond to call events in real time.
• Twilio Studio – Build call flows visually without code.

If you’re new to Twilio, the free trial gives you a $15 credit and a dedicated phone number to experiment with.

ElevenLabs: The TTS Engine That Sounds Human

ElevenLabs delivers one of the most natural TTS voices available today, with support for dozens of languages and accents. Its deep‑learning models can even clone a speaker’s voice from a short sample, making personalized voice experiences a reality.

Why ElevenLabs?

• Ultra‑realistic audio – Neural models that mimic human prosody.
• Voice cloning – Create a custom voice in minutes.
• API‑first – Simple REST endpoints that fit neatly into any stack.

If you’re looking to create a voice‑rich application, ElevenLabs is the go‑to choice. Try it out with this link: https://try.elevenlabs.io/kr07zfuqn1bp

Putting It Together: Twilio + ElevenLabs

Below is a step‑by‑step guide to building a simple outbound call that reads a custom message using ElevenLabs’ TTS service.

1. Set Up Your Twilio Account

1. Sign up for Twilio and grab your Account SID and Auth Token from the console.
2. Buy a phone number (or use the trial number).
3. Install the Twilio helper library for your language of choice.

# Python
pip install twilio

2. Create an ElevenLabs TTS Endpoint

ElevenLabs provides a straightforward REST API. You’ll need an API key, which you can obtain from the ElevenLabs dashboard.

# Example: Python
import requests

ELEVEN_API_KEY = 'YOUR_ELEVEN_API_KEY'
text = "Hello, this is your friendly voice assistant."

response = requests.post(
    'https://api.elevenlabs.io/v1/text-to-speech',
    headers={'xi-api-key': ELEVEN_API_KEY},
    json={
        'text': text,
        'voice_settings': {'pitch': 0, 'rate': 0}
    }
)

audio_url = response.json()['audio_url']
print(audio_url)

The endpoint returns a URL pointing to the generated MP3. You can stream or download this file as needed.

3. Build a TwiML Response

Twilio expects an XML (TwiML) payload that tells it what to do during a call. In this example, we’ll stream the audio from ElevenLabs directly.

from twilio.twiml.voice_response import VoiceResponse, Play

def twiml_response(audio_url):
    resp = VoiceResponse()
    resp.play(url=audio_url)
    return str(resp)

# Example usage in a Flask route
from flask import Flask, request, Response

app = Flask(__name__)

@app.route("/voice", methods=['POST'])
def voice():
    # Call ElevenLabs to get audio
    audio_url = get_elevenlabs_audio()  # Your function from step 2
    twiml = twiml_response(audio_url)
    return Response(twiml, mimetype='text/xml')

4. Trigger the Call from Twilio

Now that we have a /voice endpoint that streams ElevenLabs audio, we can instruct Twilio to call a number and hit that endpoint.

from twilio.rest import Client

client = Client('YOUR_ACCOUNT_SID', 'YOUR_AUTH_TOKEN')

call = client.calls.create(
    to='[phone]',
    from_='[phone]',  # Your Twilio number
    url='https://yourdomain.com/voice'  # HTTPS endpoint
)

print(call.sid)

When the call connects, Twilio will request the /voice URL, receive the TwiML, and play the ElevenLabs‑generated voice.

Advanced: Voice Cloning in Real Time

One of the coolest features of ElevenLabs is voice cloning. Suppose you want your app to speak in a user‑defined voice. Here’s a quick sketch of how you could do that.

def clone_voice(sample_audio_url):
    # Upload a short sample (max 30 seconds)
    with open('sample.wav', 'rb') as f:
        files = {'audio_file': f}
        response = requests.post(
            'https://api.elevenlabs.io/v1/voices',
            headers={'xi-api-key': ELEVEN_API_KEY},
            files=files
        )
    return response.json()['voice_id']

# Later, use the cloned voice_id in text-to-speech
def text_to_speech_with_clone(text, voice_id):
    response = requests.post(
        'https://api.elevenlabs.io/v1/text-to-speech',
        headers={'xi-api-key': ELEVEN_API_KEY},
        json={
            'text': text,
            'voice_id': voice_id,
            'voice_settings': {'pitch': 0, 'rate': 0}
        }
    )
    return response.json()['audio_url']

Integrate this into your TwiML flow, and you’ll have a truly personalized call experience.

Testing Locally with Ngrok

If you’re running your server locally, expose it to the internet with Ngrok so Twilio can reach it.

ngrok http 5000

Copy the HTTPS URL and set it as the webhook in your Twilio console or in the client.calls.create URL parameter.

Deployment Tips

• Secure your endpoints – Use Twilio’s request validation to ensure only Twilio can hit your webhook.
• Use environment variables – Store your API keys and Twilio credentials securely.
• Cache audio – ElevenLabs’ TTS calls cost per request; caching the MP3 URLs can save money and latency.

Wrap‑Up

You’ve now seen how to combine Twilio’s telephony power with ElevenLabs’ state‑of‑the‑art TTS to build a voice call application that sounds natural and even personalized. Whether you’re creating a customer support bot, a notification system, or a voice‑enabled game, this stack gives you the flexibility and quality you need.

If you’re ready to take your voice app to the next level, give ElevenLabs a try and see how its realistic voices can transform your user experience. 👉 https://try.elevenlabs.io/kr07zfuqn1bp

Happy coding!