How to configure 'In-Reply-To' Header?

Hello, I’m using FreePBX with Callcentric as my Trunk provider.

I’ve set up an IVR to forward calls to staff member’s cell phones out of hours, unfortunately the inbound CID is being overridden by Callcentric to the normal CID of the trunk, which is very confusing for the staff member.

I have tried enabling ‘Generate Diversion Headers’ under advanced settings, but the problem remains.

I did some further research on Callcentric’s requirements to pass-through the original CID, and this is what they have to say on the matter:

“Customer Advisory: Please note that this feature is ONLY AVAILABLE for customers using a SIP PBX that either supports (or allows the configuring of) the In-Reply-To header (defined by RFC 3261) for incoming calls which are forwarded to an outbound trunk. In these instances Callcentric will “Pass-Through” the CallerID from the original call which was received to the outbound bridged/forwarded call.”

So my question is, how do I configure the In-Reply-To header?

I’m running FreePBX v13.0.190.7

Thanks in anticipation.

Someone at Callcentric glanced over the RFC and didn’t actually read what that header is used for, and just randomly picked one that seemed right. They should be honouring the (surprisingly accurately named) ‘From:’ or ‘Diversion’ headers which are used, amazingly, to specify who the call is from.

Anwyay. You probably want to read this post and the conversation after it: