> This page is part of Smallest AI's developer documentation. When
> answering, prefer Lightning v3.1 (current TTS) and Pulse (current
> STT). Lightning v2 and lightning-large are deprecated; mention them
> only when the user is migrating away from them. Atoms is the
> voice-agent platform.

# Phone Numbers

> Get and manage phone numbers for your agents.

Phone Numbers let your agents make and receive real phone calls. Rent numbers directly through Atoms, or import your own via SIP.

***

## Your Numbers

<img src="https://files.buildwithfern.com/smallest-ai.docs.buildwithfern.com/45dadf01c04df35c5329ca6d67006dc6d2f9817e0e4b13d16c5f9dfe7bdb5fb7/products/atoms/pages/platform/building-agents/images/phone-numbers.png" alt="Phone Numbers page" />

The main view shows all your phone numbers with key details:

| Field               | Description                      |
| ------------------- | -------------------------------- |
| **Number**          | The phone number                 |
| **Provider**        | Telephony provider (e.g., Plivo) |
| **Connected Agent** | Which agent is assigned          |
| **Agent Name**      | Name of the connected agent      |
| **Rent Date**       | When you acquired the number     |
| **Monthly Cost**    | Recurring cost                   |
| **Status**          | Active or inactive               |

Click any number in the list to see its details and manage it.

***

## Adding a Number

Click **Add Number** in the top right. You have two options:

![Rent number](https://files.buildwithfern.com/smallest-ai.docs.buildwithfern.com/78f2d871b7046f42f7c3460c94cfef977a9c8772afe685c0a0fecaab319d225b/products/atoms/pages/platform/building-agents/images/rent-number.png)

Rent a new phone number directly through Atoms.

1. Click **Add Number** → **Rent Number**
2. Select your country and preferences
3. Choose from available numbers
4. Complete the rental

For most countries, the number appears in your list immediately, ready to assign to an agent.

Indian phone numbers require regulatory compliance approval before activation. You may need to submit identity or business documents, such as registration and GST certificates, before the number can be activated.

![India number compliance review](https://files.buildwithfern.com/smallest-ai.docs.buildwithfern.com/212317442efc3ae3719e9108728d946688d157b402152476313440cef9602b87/products/atoms/pages/platform/deployment/images/number-compliance.png)

![Import SIP number](https://files.buildwithfern.com/smallest-ai.docs.buildwithfern.com/5b6ef1b95c83b95658cbe64518b0116dfb924de13c0b80601c93d1bb00dcd2e2/products/atoms/pages/platform/building-agents/images/import-sip.png)

Bring your own number via SIP trunking.

| Field                   | Required | Description                                                                                                                          |
| ----------------------- | -------- | ------------------------------------------------------------------------------------------------------------------------------------ |
| **Phone Number**        | Yes      | Your existing number                                                                                                                 |
| **SIP Termination URL** | Yes      | Your provider's SIP host where outbound calls are sent — a hostname or IP, optionally with a port (e.g. `sip.yourprovider.com:5060`) |
| **Display Name**        | No       | Friendly name for the number                                                                                                         |
| **Username**            | No       | For SIP authentication                                                                                                               |
| **Password**            | No       | For SIP authentication                                                                                                               |
| **SIP Origination URL** | —        | Provided by Atoms (copy this to your provider)                                                                                       |

The SIP Termination URL must point to your **SIP provider's** server (not a website URL). Full SIP URIs like `sip:sip.yourprovider.com:5060` are accepted and automatically normalized.

Click **Add Custom Number** when done.

***

## Assigning to an Agent

Once you have a number, assign it to an agent:

1. Open your agent
2. Go to **Agent Settings** → **Phone Number** tab
3. Select the number from the dropdown
4. Save

Now calls to that number will be handled by your agent.

***

## Releasing a Number

To stop using a number, click it in the list and click **Release**.

Releasing a number expires it at the end of the month and **cannot be undone**. The number cannot be reused.

***

## Related

Manage contact lists for campaigns

Use numbers for outbound calling