### Answer To display the original caller's number (transferee's number) as the caller ID when transferring calls with Twilio, the behavior differs between warm and cold transfers: ## Warm Transfer For warm transfers, Retell uses SIP DIAL and sets the

from

and

P-Asserted-Identity

headers to the user's number. [(1) ]() [(2) ]() Retell Twilio numbers support showing the user's number on both warm and cold transfers. ## Cold Transfer For cold transfers, Retell uses SIP REFER, and it's up to the telephony provider to support caller ID override for SIP REFER. Important limitation: Twilio does not honor custom SIP headers in the REFER request, so the SIP headers you set in the transfer call tool will not work for cold transfer with transferee number when using Twilio. [(3) ]() ## Configuration Steps In your Transfer Call function or Call Transfer Node, select "Transferee's Number" as the displayed phone number option. [(1) ]() [(2) ]() However, for this to work with Twilio cold transfers, your Twilio configuration must have: [(4) ]() - Enable SIP REFER - Enable transfer to PSTN - Set caller ID as transferee ## Recommendation If you need the original caller's number to display reliably with Twilio, use warm transfer instead of cold transfer, as warm transfer provides more control and Twilio supports caller ID override for warm transfers. [(1) ]() [(2) ](

/transfer-call) [(4) ]()

​ To learn more, see the sources I considered: [[1] Call Transfer Node](https://docs.retellai.com/build/conversation-flow/call-transfer-node) [[2] Transfer call](https://docs.retellai.com/build/single-multi-prompt/transfer-call) [[3] Set & parse custom SIP headers](https://docs.retellai.com/build/telephony/sip-headers) [[4] Help on Twilio DID questions](https://community.retellai.com/t/help-on-twilio-did-questions/24) ​

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