Elastic SIP Trunking does not alter the Caller ID for calls:
- Outgoing calls on a Twilio Elastic SIP trunk (SIP Termination) must use a valid Twilio phone number owned on this project, or a verified Caller ID (using E.164 formatting).
- Incoming calls on a Twilio Elastic SIP trunk (SIP Origination) will have the originating caller ID Twilio receives passed along with the SIP INVITE (using E.164 formatting).
This being said, it's possible for Caller IDs in general to be changed in transit for a number of reasons. For more details, please see the following resources: