Add docs for outbound calls with twilio (#273)

* Add docs for outbound calls with twilio

* Add code

---------

Co-authored-by: Freddy Boulton <41651716+freddyaboulton@users.noreply.github.com>

docs/userguide/audio.md

@@ -386,3 +386,48 @@ stream.mount(app)
 
 # run with `uvicorn main:app`
 ```
+
+### Outbound calls with Twilio
+
+Here's a simple example to call someone using the twilio-python module:
+
+```py
+app = FastAPI()
+
+@app.post("/call")
+async def start_call(req: Request):
+  body = await req.json()
+  from_no = body.get("from")
+  to_no = body.get("to")
+  account_sid = os.getenv("TWILIO_ACCOUNT_SID")
+  auth_token = os.getenv("TWILIO_AUTH_TOKEN")
+  client = Client(account_sid, auth_token)
+
+  # Use the public URL of your application
+  # here we're using ngrok to expose an app
+  # running locally
+  call = client.calls.create(
+    to=to_no,
+    from_=from_no,
+    url="https://[your_ngrok_subdomain].ngrok.app/incoming-call"
+  )
+
+  return {"sid": f"{call.sid}"}
+
+@app.api_route("/incoming-call", methods=["GET", "POST"])
+async def handle_incoming_call(req: Request):
+  from twilio.twiml.voice_response import VoiceResponse, Connect
+  response = VoiceResponse()
+  response.say("Connecting to AI assistant")
+  connect = Connect()
+  connect.stream(url=f'wss://{req.url.hostname}/media-stream')
+  response.append(connect)
+  return HTMLResponse(content=str(response), media_type="application/xml")
+
+@app.websocket("/media-stream")
+async def handle_media_stream(websocket: WebSocket):
+  # stream is a FastRTC stream defined elsewhere
+  await stream.telephone_handler(websocket)
+
+app = gr.mount_gradio_app(app, stream.ui, path="/")
+```