[SR-Users] Should a proxy change Contact or From domains?

Hi all, Theoretical question about the role of a Kamailio proxy which is also a registration server for UAs. Assuming a B2BUA on IP 1.2.3.4 behind the Kamailio proxy. Kamailio receives an INVITE from this B2BUA with From and Contact as something like sip:4321@1.2.3.4 When Kamailio routes the INVITE to that UA, is it Kamailio’s responsibility to change the domain part of the From and/or Contact to itself (e.g. sip:4321@proxy.mytld.com)? The question has arisen from Polycom missed call “call back” behaviour. When issuing a call back from a Polycom, following a missed call, it sends the call directly to the full URI in the INVITE’s From (or maybe Contact… I’ve not fully tested yet). As such the call is sent to the B2BUA, which UAs do not have access to, and thus times out. I suspect here the answer is “no”, and the Polycom must be configured to force all outbound calls through the proxy… but thoughts welcome. Cheers Phil