By registering trunk, I mean a trunk between a PBX and Kamailio, of say 15 DID's, where the main DID (Pilot) registers with Kamailio and all the other 14 DID are able to make/receive calls without having to register all DID's individually.

If the pilot DID registration goes away, the trunk is then considered to be unreachable/down.

I have seen this in the past with a Broadsoft setup, but I can't figure out a way to do it with Kamailio. 

I have my pilot DID setup and registered with Kamailio ok and I can make calls in and out through my PSTN gateway, but I'm unsure how to group all the other DID's so they are matched against the pilot DID.

Is this possible? Any help is appreciated.

Regards,

Andrei.