> ## Documentation Index
> Fetch the complete documentation index at: https://docs.millis.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# SIP Trunking

> Connecting Phone Numbers to Millis via SIP

# Overview

Millis provides seamless integration for connecting your phone system to its AI-powered voice agents using SIP. This guide walks you through the process of rerouting phone calls to Millis via SIP.

# Step-by-Step Process

## 1. Make a POST Request to `/register_sip_call`

To initiate a call, send a POST request to the `/register_sip_call` API endpoint. Depending on your location, select either the **EU-West** or **US-West** region for lower latency:

* **EU-West:** `https://api-eu-west.millis.ai/register_sip_call`
* **US-West:** `https://api-west.millis.ai/register_sip_call`

### Request Body

You must include the necessary parameters in your request body, with the option to customize agent behavior and include metadata if needed.

**Request Body Example:**

```json theme={null}
{
  "agent_id": "your_agent_id",
  "agent_config": {
    config options for the agent
  },
  "metadata": {
    "key": "value"
  },
  "include_metadata_in_prompt": true
}
```

**Field Details:**

* `agent_id`: *(Optional)* The ID of the Millis AI agent that will handle the call.
* `agent_config`: *(Optional)* Configuration options for the agent, allowing you to customize behavior.
  * If both `agent_id` and `agent_config` are provided, the parameters in `agent_config` will override the original parameters for the agent tied to `agent_id`.
  * You can also provide just `agent_config` for a temporary configuration, which will be used to construct an agent to handle the call.
* `metadata`: *(Optional)* Any additional information to attach to the session, giving the agent context to enhance its response. To learn more about how metadata works, visit the [Metadata Guide](/core-concepts/metadata).
* `include_metadata_in_prompt`: *(Optional)* Boolean value indicating if the metadata should be included in the agent's conversational prompt.

# 2. Receive the SIP URI

After making the POST request, you will receive a response containing a `call_id` and a `sip_uri`. This `sip_uri` is the address you will use to route your phone calls to Millis.

**Response Example:**

```json theme={null}
{
  "call_id": "unique_call_id",
  "sip": "sip:call-uniqueid@<millis-sip-server>"
}
```

# 3. Reroute Your Call

Use the provided `sip_uri` to reroute the call from your phone system to Millis. Your phone system will forward the call audio to Millis, where the voice agent can interact with the caller.