Modifying Diversion header
edit - I've edited below quite a lot because it was actually working :-)
We receive an INV in the following format:
INVITE sip:3035558010-csv10580vgmb0@192.168.223.4:5060;transport=udp SIP/2.0 Via:SIP/2.0/UDP 192.168.223.193;branch=z9hG4bK-BroadWorks.node1-192.168.223.4V5060-0-651503064-734754704-1369250089902- From:"pstn user"<sip:6785557626@192.168.223.193;user=phone>;tag=734754704-1369250089902- To:"subscriber1"<sip:3035558010@voip.com> Call-ID:BW191449902220513-1124318947@192.168.223.193 CSeq:651503064 INVITE Contact:<sip:192.168.223.193:5060> Diversion:"subscriber2"<sip:3035558011@192.168.223.193;user=phone>;reason=user-busy;counter=1,"subscriber3"<sip:3035558008@192.168.223.193;user=phone>;reason=user-busy;counter=1 Allow:ACK,BYE,CANCEL,INFO,INVITE,OPTIONS,PRACK,REFER,NOTIFY,UPDATE Accept:multipart/mixed,application/media_control+xml,application/sdp Call-Info:<sip:192.168.223.193>;appearance-index=1 Supported: Max-Forwards:10 Content-Type:application/sdp Content-Disposition:session;handling=required Content-Length:285