### Answer The issue you're experiencing with the '0266696687' anonymous caller ID is a telephony network behavior rather than a Retell AI-specific issue. This is how telecommunications carriers handle calls where the caller has blocked or hidden their caller ID. When you use Twilio with Retell AI via SIP trunking, the call routing works as follows: calls connect through Twilio's elastic SIP trunk to Retell AI's SIP server at

sip:sip.retellai.com

[(1) ]() [(2) ]() . The caller ID information is passed through this connection from the originating carrier through Twilio to Retell. When a caller blocks their number, the originating carrier or Twilio may substitute the placeholder '0266696687' (ANONYMOUS on a phone keypad) instead of providing the actual caller ID. This happens at the carrier/Twilio level before the call reaches Retell AI. To address this: 1. Check Twilio's call logs to see how the caller ID appears in their system - this will confirm whether the anonymous number is coming from the upstream carrier or being modified by Twilio [(1) ]() 2. Review your Twilio SIP trunk configuration - specifically the origination settings that handle inbound calls to ensure caller ID information is being passed through correctly 3. Consider implementing caller ID verification - you could use Retell AI's call handling to screen or handle anonymous callers differently through your agent configuration The anonymous caller ID behavior is standard telephony practice and not caused by Retell AI's integration. The system simply receives and processes whatever caller ID information Twilio provides through the SIP connection [(1) ]() [(2) ]() .

​ To learn more, see the sources I considered: [[1] Twilio](https://docs.retellai.com/deploy/twilio) [[2] Custom Telephony Overview](https://docs.retellai.com/deploy/custom-telephony) ​

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