### Answer Yes, you can integrate RingCentral numbers with Retell AI for inbound calls using custom telephony via SIP trunking [(1) ]() . Retell supports two integration methods : *Method 1: Elastic SIP Trunking (Recommended) * This is the recommended approach where you set up SIP trunking with RingCentral and configure your numbers to point to it, then import those numbers into Retell . When using elastic SIP trunking, all telephony functionalities supported by Retell numbers will also work here, assuming RingCentral supports them . Method 2: Dial to SIP URI If RingCentral doesn't support elastic SIP trunking or you have a more complex setup, you can dial calls to Retell's SIP server URI:

sip:sip.retellai.com

. Retell's SIP server details: - IP block for traffic:

18.98.16.120/30

(All regions) ,

143.223.88.0/21

(certain US traffic) ,

161.115.160.0/19

(certain US traffic) - Supported transport methods: TCP (Recommended) , UDP, TLS After setting up SIP trunking with RingCentral, you would import your phone numbers into Retell using the Import Phone Number API [(2) ]() . You'll need to provide the phone number in E.164 format and the termination URI to identify your elastic SIP trunk .

​ To learn more, see the sources I considered: [[1] Custom Telephony Overview](https://docs.retellai.com/deploy/custom-telephony) [[2] Import Phone Number](https://docs.retellai.com/api-references/import-phone-number) ​

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