Does 3CX support echoing Twilio's X-Twilio-CallToken header for Immutable Call Forwarding?

[[email protected]]

Running 3CX V20, self-hosted, with a Twilio Elastic SIP Trunk. We're trying to preserve the original caller's number when forwarding after-hours calls to a third-party answering service over PSTN.


Twilio confirmed our use case requires their new Immutable Call Forwarding with CallToken feature (public beta, announced June 2026). This requires the PBX to:

1. Receive the X-Twilio-CallToken SIP header on the inbound trunk call
2. Echo that same header back on the outbound forwarded INVITE
3. Set From/P-Asserted-Identity to the original caller's number on that leg

Question: Does 3CX currently support passing through/echoing a custom SIP header like this from an inbound call to an outbound forwarded call — natively, via template customization, or otherwise? Haven't found any documentation or threads on this yet.

 

[KyriacosS_3CX]

Hello,

We do not currently support this or in general any non-standard headers. If you believe this is important you can ask a partner of the appropriate level to suggest it in the ideas forum.

 

[Charles_3CX]

In addition to my colleague's reply, it is possible to modify the template to pass the originator's caller ID to whichever SIP field the provider uses to present the caller ID, provided that the originator's caller ID is received in a SIP header that is currently available.

However, based on our testing with Twilio, they have confirmed that they do not support CLIP no-screening. Therefore, they will fail the call if the caller ID number being presented is not associated with your Twilio account.

 

[Evolute IT]

The new SIP REFER function in 3CX might work here. Twilio does support that.

https://www.twilio.com/docs/sip-trunking/call-transfer