---
name: text-to-speech-phone-call
title: "Text to Speech Phone Call"
description: "Play text-to-speech audio during a phone call."
language: python
framework: flask
telnyx_products: [Voice]
---

# Production-ready Flask application for text-to-speech calls via Telnyx.

Production-ready Flask application for text-to-speech calls via Telnyx.

## Telnyx API Endpoints Used

- **Call Control: Answer**: `POST /v2/calls/{id}/actions/answer` — [API reference](https://developers.telnyx.com/api/call-control/answer-call)
- **Call Control: Speak (TTS)**: `POST /v2/calls/{id}/actions/speak` — [API reference](https://developers.telnyx.com/api/call-control/speak)

## Telnyx Webhook Events

This app handles these webhook events ([Call Control docs](https://developers.telnyx.com/docs/api/v2/call-control)):

- `call.answered` — Call connected — app begins interaction
- `call.hangup` — Call ended — app cleans up session, triggers post-call processing
- `call.initiated` — New inbound or outbound call detected
- `call.speak.ended` — TTS playback finished — app transitions to next action (gather, transfer, etc.)

## Architecture

```
  Inbound Phone Call
        │
        ▼
  ┌──────────────────┐
  │ Call Control      │
  └────────┬─────────┘
           │
           ├──► TTS
           │
           ▼
     Voice response
```

## Environment Variables

Copy `.env.example` to `.env` and fill in:

| Variable | Type | Example | Required | Description | Where to get it |
|----------|------|---------|----------|-------------|-----------------|
| `TELNYX_API_KEY` | `string` | `KEY0123456789ABCDEF` | **yes** | Telnyx API v2 key | [Portal](https://portal.telnyx.com/api-keys) |
| `TELNYX_PHONE_NUMBER` | `string` | `your_value` | **yes** | Telnyx phone number | — |
| `TELNYX_CONNECTION_ID` | `string` | `your_value` | **yes** | Telnyx connection id | — |
| `FLASK_DEBUG` | `string` | `false` | no | Flask debug | — |

## Setup

```bash
git clone https://github.com/team-telnyx/telnyx-code-examples.git
cd telnyx-code-examples/text-to-speech-phone-call-python
cp .env.example .env    # ← fill in your credentials
pip install -r requirements.txt
python app.py           # starts on http://localhost:5000
```

### Webhook Configuration

1. Expose your local server:

   ```bash
   ngrok http 5000
   ```

2. Copy the HTTPS URL and configure in [Telnyx Portal](https://portal.telnyx.com):

   - **Call Control Application** → Webhook URL → `https://<id>.ngrok.io/webhooks/voice`

## API Reference

### `POST /calls/initiate`

HTTP endpoint to initiate an outbound call.

```bash
curl -X POST http://localhost:5000/calls/initiate \
  -H "Content-Type: application/json" \
  -d '{
    "to": "+12125551234"
  }'
```

**Response:**

```json
{
  "call_id": "v3:uMi2qMWHT-mLFGkEm4t9tA",
  "status": "initiated",
  "from": "+18005551234",
  "to": "+12125559876"
}
```

### `POST /calls/<call_control_id>/speak`

HTTP endpoint to play TTS on an active call.

```bash
curl -X POST http://localhost:5000/calls/example-id/speak \
  -H "Content-Type: application/json" \
  -d '{
    "to": "+12125551234"
  }'
```

**Response:**

```json
{
  "call_id": "v3:uMi2qMWHT-mLFGkEm4t9tA",
  "status": "initiated",
  "from": "+18005551234",
  "to": "+12125559876"
}
```

### `POST /calls/<call_control_id>/hangup`

HTTP endpoint to terminate a call.

```bash
curl -X POST http://localhost:5000/calls/example-id/hangup \
  -H "Content-Type: application/json" \
  -d '{
    "to": "+12125551234"
  }'
```

**Response:**

```json
{
  "call_id": "v3:uMi2qMWHT-mLFGkEm4t9tA",
  "status": "initiated",
  "from": "+18005551234",
  "to": "+12125559876"
}
```

### `GET /calls/status`

HTTP endpoint to retrieve status of all active calls.

```bash
curl http://localhost:5000/calls/status
```

**Response:**

```json
{
  "calls": [
    {
      "call_id": "v3:uMi2qMWHT-mLFGkEm4t9tA",
      "from": "+18005551234",
      "to": "+12125559876",
      "duration_seconds": 145,
      "status": "completed"
    }
  ]
}
```

## Webhook Endpoints

### `POST /webhooks/call`

Receives [Telnyx Call Control](https://developers.telnyx.com/docs/voice/call-control) webhook events.

**Events handled:** `call.answered`, `call.hangup`, `call.initiated`, `call.speak.ended`

**Example payload:**

```json
{
  "data": {
    "event_type": "call.initiated",
    "id": "0ccc7b54-4df3-4bca-a65a-3da1ecc777f0",
    "occurred_at": "2026-07-15T14:30:00.000Z",
    "payload": {
      "call_control_id": "v3:uMi2qMWHT-mLFGkEm4t9tA",
      "connection_id": "1494404757140276705",
      "call_leg_id": "428c31b6-7af4-4bcb-b7f5-5013ef9657c1",
      "call_session_id": "428c31b6-abcd-1234-5678-5013ef9657c1",
      "client_state": null,
      "from": "+12125551234",
      "to": "+13105559876",
      "direction": "incoming",
      "state": "ringing"
    },
    "record_type": "event"
  },
  "meta": {
    "attempt": 1,
    "delivered_to": "https://your-server.example.com/webhooks/voice"
  }
}
```

## Troubleshooting

| Issue | Cause | Fix |
|-------|-------|-----|
| `401 Unauthorized` | Invalid or missing API key | Verify `TELNYX_API_KEY` in `.env` matches your key in the [Portal](https://portal.telnyx.com/api-keys) |
| Webhook not received | Local server not publicly reachable | Expose it with a tunnel (e.g. ngrok) and set the webhook URL in the [Telnyx Portal](https://portal.telnyx.com) |
| `422 Unprocessable Entity` | Missing or malformed request fields | Check the request body against the API Reference above |

## Related Examples

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- [Build Conference Calling (Python)](https://raw.githubusercontent.com/team-telnyx/telnyx-code-examples/main/build-conference-calling-python/README.md)
- [Build IVR Phone Menu (Python)](https://raw.githubusercontent.com/team-telnyx/telnyx-code-examples/main/build-ivr-phone-menu-python/README.md)
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## Resources

- [Call Control Guide](https://developers.telnyx.com/docs/voice/call-control)
- [Telnyx Developer Docs](https://developers.telnyx.com)
- [Telnyx Portal](https://portal.telnyx.com)

## Why Telnyx

Telnyx is an **AI Communications Infrastructure** platform — voice, messaging, SIP, AI, and IoT on one private, global network.