ElevenLabs + Twilio: Building Voice Call Applications

Why combine ElevenLabs and Twilio?

If you’ve ever wanted to give your users a truly personal voice experience—think automated support lines, interactive storytelling, or dynamic notifications—pairing ElevenLabs’ state‑of‑the‑art text‑to‑speech (TTS) with Twilio’s programmable voice platform is a match made in the cloud.

• ElevenLabs provides ultra‑realistic voice cloning and a fast REST API that can turn any string into a high‑quality audio file in seconds.
• Twilio lets you make, receive, and control phone calls programmatically, delivering the audio to any PSTN or SIP endpoint.

Together, you can generate a custom voice on the fly and pipe it straight into a live call, all with just a few lines of code.

What you’ll need

Quick tip: If you haven’t tried ElevenLabs yet, you can sign up through this affiliate link: https://try.elevenlabs.io/kr07zfuqn1bp – it’s the same product, just a convenient way to get started.

Generating speech with ElevenLabs

ElevenLabs exposes a simple /v1/text-to-speech/{voice_id} endpoint. Here’s a minimal Python function that sends a prompt and returns a URL to the generated MP3.

import requests import os ELEVEN_API_KEY = os.getenv("ELEVEN_API_KEY") VOICE_ID = "EXAVITQu4vr4xnSDxMaL" # default “Rachel” voice; replace with your cloned voice ID  def generate_speech(text: str) -> str: url = f"https://api.elevenlabs.io/v1/text-to-speech/{VOICE_ID}" headers = { "xi-api-key": ELEVEN_API_KEY, "Content-Type": "application/json" } payload = { "text": text, "model_id": "eleven_monolingual_v1", "voice_settings": { "stability": 0.75, "similarity_boost": 0.85 } } resp = requests.post(url, json=payload, headers=headers) resp.raise_for_status() # The API returns raw audio bytes; we’ll store them in a temporary file.  filename = f"/tmp/{hash(text)}.mp3" with open(filename, "wb") as f: f.write(resp.content) return f"file://{filename}" 

A few things to note:

1. Voice cloning – If you’ve uploaded a custom voice to ElevenLabs, replace VOICE_ID with that ID. The same endpoint works for both built‑in and cloned voices.
2. Stability & similarity – Tweak these numbers to make the voice sound more expressive or more faithful to the source speaker.
3. File handling – In production you’d probably upload the MP3 to a CDN (S3, Cloudflare R2, etc.) and return a public URL. Twilio can only stream from an HTTP(S) address, not a file:// path.

Serving the audio to Twilio

Twilio expects a publicly reachable URL that returns a media file with a supported MIME type (audio/mpeg, audio/wav, etc.). A quick Flask route can bridge the gap:

from flask import Flask, request, send_file, abort import uuid app = Flask(__name__) # In‑memory map: request_id → local file path audio_store = {} @app.route("/speak", methods=["POST"]) def speak(): data = request.json if not data or "text" not in data: abort(400, "Missing 'text' field") # Generate speech and keep a reference  audio_url = generate_speech(data["text"]) request_id = str(uuid.uuid4()) audio_store[request_id] = audio_url.replace("file://", "") # Return a TwiML response that tells Twilio where to fetch the audio  twiml = f"""<?xml version="1.0" encoding="UTF-8"?> <Response> <Play>{request.host_url}audio/{request_id}</Play> </Response>""" return twiml, 200, {"Content-Type": "application/xml"} @app.route("/audio/<uid>") def serve_audio(uid): path = audio_store.get(uid) if not path or not os.path.exists(path): abort(404) return send_file(path, mimetype="audio/mpeg") 

When Twilio hits /speak with a JSON payload like {"text":"Hello, this is a test!"}, the endpoint:

1. Calls ElevenLabs to synthesize the voice.
2. Stores the resulting MP3 locally (or you could upload it to a CDN).
3. Returns TwiML that instructs Twilio to <Play> the generated file.

Wiring it up with Twilio

1. Create an outbound call webhook

In the Twilio Console, go to Phone Numbers → Manage → Active Numbers, select your number, and set the Voice & Fax → A CALL COMES IN webhook to point at your /speak endpoint, e.g.:

https://my‑app.example.com/speak 

Make sure the request method is POST (the Flask route expects JSON).

2. Trigger a call from your code

You can launch a call from anywhere—your backend, a CLI script, or even a Zapier action. Here’s a simple Python snippet using twilio-python:

from twilio.rest import Client import os TWILIO_SID = os.getenv("TWILIO_ACCOUNT_SID") TWILIO_TOKEN = os.getenv("TWILIO_AUTH_TOKEN") client = Client(TWILIO_SID, TWILIO_TOKEN) call = client.calls.create( to="+15551234567", # Destination number  from_="+15557654321", # Your Twilio number  url="https://my-app.example.com/speak", # TwiML webhook  method="POST", # Optional: pass the text you want spoken as a query param or body  # Twilio will POST it to your endpoint; you can read it there. ) print(f"Call SID: {call.sid}") 

When the call connects, Twilio will request the /speak endpoint, which in turn will ask ElevenLabs to generate the audio and then play it back to the callee.

Going further: streaming instead of pre‑saving

If you need near‑real‑time responses (e.g., a chatbot that replies instantly), you can stream the ElevenLabs audio directly to Twilio using Twilio Media Streams. The idea is:

1. Open a WebSocket from Twilio to your server (<StartStream> TwiML).
2. Pipe the binary audio chunks from ElevenLabs into that socket.

While the full implementation is beyond the scope of this article, the pattern looks like this:

<Response> <StartStream name="myStream" url="wss://my-app.example.com/stream"/> <Pause length="1"/> <!-- give the stream a moment to connect --> <Say voice="alice">Listening...</Say> </Response> 

Your WebSocket handler would receive the text you want spoken, call ElevenLabs with the streaming endpoint (/v1/text-to-speech/{voice_id}/stream), and forward each chunk back to Twilio. This yields sub‑second latency and feels truly conversational.

Tips & best practices

Putting it all together

Below is a minimal end‑to‑end flow diagram:

User → (Dial) Twilio → (POST) /speak → generate_speech() → ElevenLabs API ↑ | | v ←——————— <Play> audio URL ←——————— (store & serve MP3) 

With the Flask app, the Twilio webhook, and the tiny twilio-python client snippet, you have a fully functional voice‑AI pipeline that can be extended to:

• IVR menus that sound like your brand’s CEO.
• Appointment reminders with a custom regional accent.
• Dynamic storytelling where each user choice generates a fresh narration.

All of this is possible with a few dozen lines of code and the powerful combination of ElevenLabs and Twilio.

Ready to give your callers a human‑like voice?

The barrier to building high‑quality voice applications has never been lower. Grab an API key, spin up a tiny Flask (or Express) service, and start experimenting. If you’re curious about how realistic voice cloning can boost engagement, try ElevenLabs today via this link: https://try.elevenlabs.io/kr07zfuqn1bp. Happy coding!