### Answer Here's a comparison between purchasing numbers directly from Retell vs. using Twilio SIP trunking: ## Retell-Purchased Numbers Benefits: - Simpler setup with no additional configuration required [(1) ]() - Carrier-verified numbers (T-Mobile, AT&T, Verizon) that reduce "Spam Likely" flags and improve answer rates - Pricing at $2/month per number - Currently supports US-based numbers only ## Twilio SIP Trunking Benefits: - Access to numbers in 100+ countries for worldwide coverage [(2) ]() - Use existing Twilio numbers/infrastructure [(3) ]() - All Retell telephony features remain supported when using elastic SIP trunking [(4) ]() - More flexibility with toll-free numbers, international numbers, and custom telephony setups [(3) ]() Setup Requirements: - Create elastic SIP trunk with termination (outbound) and origination (inbound) settings - Set origination SIP URI to

sip:sip.retellai.com

- Configure authentication via IP whitelisting or credentials - Import numbers to Retell with termination URI - Use localized termination URIs near your region for better performance ## Latency Considerations One community member reported observing ~1800ms latency on SIP vs. 1000-1400ms on direct Twilio numbers, suggesting SIP may introduce some additional latency depending on configuration [(5) ]() . Using a localized termination URI near your region is recommended to optimize performance [(3) ]() . #

# Worldwide Use For international calling via Twilio SIP trunk, you'll need to enable "Voice Geographic Permissions" in Twilio and select the countries you want to dial . Summary: Retell numbers offer simplicity and verified caller ID for US operations. Twilio SIP trunking provides global reach and flexibility with existing infrastructure, but requires more configuration.

​ To learn more, see the sources I considered: [[1] AI Phone Numbers: How to Buy & Set Up | Retell AI](https://www.retellai.com/blog/how-to-buy-an-ai-phone-number-a-guide-on-your-options-and-providers) [[2] AI in SIP Calling & Telephony Solutions | Retell AI](https://www.retellai.com/blog/integrating-ai-with-sip-trunking-and-modern-telephony) [[3] Twilio](https://docs.retellai.com/deploy/twilio) [[4] Custom Telephony Overview](https://docs.retellai.com/deploy/custom-telephony) [[5] Discord message from @.teamrick on 2024-10-18](https://discord.com/channels/1186424376300679209/1294891368505937952/1296927174703714335) ​

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