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

# Phone numbers

> Connect phone numbers to your agents for inbound and outbound calls.

Cartesia supports three ways to connect phone numbers to your agents: Cartesia-provisioned numbers, numbers imported from Twilio, and numbers connected through your SIP carrier.

Agent calling rates apply to all three options. Cartesia charges an additional telephony fee only when you use a Cartesia-provisioned number.

| Feature                | Cartesia numbers    | Twilio numbers                                                       | SIP trunk numbers                           |
| ---------------------- | ------------------- | -------------------------------------------------------------------- | ------------------------------------------- |
| Number origin          | US only             | Any country available in Twilio                                      | Any country available from your carrier     |
| Inbound calls          | ✓                   | ✓                                                                    | ✓ with inbound configured                   |
| Outbound to US         | ✓                   | ✓                                                                    | ✓ with outbound configured                  |
| Outbound international | ✗                   | ✓ at your Twilio cost                                                | Carrier-dependent, with outbound configured |
| Regional routing       | N/A                 | [Configurable](/line/integrations/telephony/twilio/regional-routing) | Carrier-dependent                           |
| Provisioning           | Automatic           | Import from Twilio                                                   | Import from your carrier                    |
| Telephony cost         | +\$0.014/min add-on | Your Twilio rates apply                                              | Your carrier rates apply                    |

<CardGroup cols={3}>
  <Card title="Cartesia numbers" icon="square-phone" href="/line/integrations/telephony/cartesia-numbers">
    Provision US numbers from Cartesia.
  </Card>

  <Card title="Twilio" icon="puzzle-piece" href="/line/integrations/telephony/twilio/integration">
    Import numbers from your Twilio account.
  </Card>

  <Card title="SIP trunk" icon="tower-broadcast" href="/line/integrations/telephony/sip-trunking">
    Connect numbers from your SIP carrier.
  </Card>
</CardGroup>

## Manage numbers

View and manage every number on the [Phone Numbers](https://play.cartesia.ai/phone-numbers) page in the Playground or through the [Phone Numbers API](/api-reference/agents/phone-numbers/list).

<Frame caption="Phone numbers in the Playground">
  <img src="https://mintcdn.com/cartesia-2650f86a/cyPOLB5BGhebR1Zv/assets/images/agents/telephony/phone-number-list.png?fit=max&auto=format&n=cyPOLB5BGhebR1Zv&q=85&s=e63d2eda17e41ce0db850f62137e6340" alt="Phone numbers page listing numbers in the Playground" width="1699" height="816" data-path="assets/images/agents/telephony/phone-number-list.png" />
</Frame>

### Assign an inbound agent

Assigning a phone number to an agent routes inbound calls on that number to the agent. A number is assigned to one agent at a time, and an agent can have several numbers.

<Tabs>
  <Tab title="Playground">
    1. Open the phone number's detail page.
    2. In the **Agent** card, search for and select your agent.
  </Tab>

  <Tab title="API">
    ```bash theme={null}
    curl -X PATCH "https://api.cartesia.ai/agents/phone-numbers/YOUR_PHONE_NUMBER_ID" \
      -H "X-API-Key: $CARTESIA_API_KEY" \
      -H "Cartesia-Version: 2026-08-14" \
      -H "Content-Type: application/json" \
      -d '{ "agent_id": "YOUR_AGENT_ID" }'
    ```

    To unassign, set `agent_id` to `null`.
  </Tab>
</Tabs>

### Outbound calls

Any number on your account can place outbound calls, whether or not it is assigned to an agent. Pass its ID as `from_number_id` when you [place an outbound call](/line/integrations/telephony/outbound-dialing).