### Answer --- Yes, you can use Retell's API to purchase numbers and attach them to specific agents programmatically. [(1) ]() ## Purchasing via API Use the [Create Phone Number API]() to purchase a number and assign agents in one call:

javascript
const phoneNumberResponse = await retell.phoneNumber.create({
 inbound_agent_id: "oBeDLoLOeuAbiuaMFXRtDOLriTJ5tSxD", // replace with the agent id you want to assign
 outbound_agent_id: "oBeDLoLOeuAbiuaMFXRtDOLriTJ5tSxD", // replace with the agent id you want to assign
}) ;
console.log(phoneNumberResponse) ;

You can assign different inbound and outbound agents to the number. ## Updating an Existing Number If you need to change the agent assignment later, use the Update Phone Number API: [(2) ]()

javascript
import Retell from 'retell-sdk';
const client = new Retell({
 apiKey: 'YOUR_RETELL_API_KEY',
}) ;
const phoneNumberResponse = await client.phoneNumber.update('+14157774444', {
 inbound_agent_id: 'oBeDLoLOeuAbiuaMFXRtDOLriTJ5tSxD',
 nickname: 'Frontdesk Number',
 outbound_agent_id: 'oBeDLoLOeuAbiuaMFXRtDOLriTJ5tSxD',
}) ;
console.log(phoneNumberResponse.inbound_agent_id) ;

Phone numbers are yours once purchased and can be used indefinitely. [(1) ]()

​ To learn more, see the sources I considered: [[1] Purchase phone number](https://docs.retellai.com/deploy/purchase-number) [[2] Update Phone Number](https://docs.retellai.com/api-references/update-phone-number) ​

Feel free to tag @AI Evy with additional questions. I also appreciate feedback, it helps me improve.

### Answer Based on the available sources, I don't have explicit documentation on whether Retell-purchased numbers can be used outside of Retell's system for other services. What the documentation does show: - Phone numbers purchased through Retell (via Twilio or Telnyx) are typed as

retell-twilio

or

retell-telnyx

[(1) ]() - These numbers are designed to bind to Retell agents for inbound and outbound calls - You can use the Register Phone Call API to integrate with custom telephony setups, but this is for routing calls to Retell agents [(2) ]() For the reverse scenario—using Retell numbers with external services while still making calls through Retell—the sources don't provide clear guidance on this use case. Check out these potentially useful sources: - [Create Phone Number]() - [Register Phone Call]() - [Import Phone Number]() Would you like me to provide a general answer based on my knowledge instead?

​ To learn more, see the sources I considered: [[1] List Phone Numbers](https://docs.retellai.com/api-references/list-phone-numbers) [[2] Register Phone Call](https://docs.retellai.com/api-references/register-phone-call) ​

Feel free to tag @AI Evy with additional questions. I also appreciate feedback, it helps me improve.