I have a v15 SP5 64SC with a 10 channel sip trunk. Everything appears to be working properly except when an external call comes in via the sip trunk, is answered at a reception extension and an attended transfer is started to the desired extension. If the called party does not answer it is set to forward to their mobile. This progresses properly and the call can be answered on the mobile phone and converse with recepetion OK but when the transfer tries to complete then the call fails with an error 480 Temporarily Unavailable message. Blow is an except from the trace done by our sip trunk provider (with identifying digits replaced). INVITE sip:04xxx6789@XXX.XXX.XXX.38:5060 SIP/2.0 Via: SIP/2.0/UDP XXX.XXX.XXX.97:5060;branch=z9hG4bK-524287-1--- 1f7be46505433776;rport Max-Forwards: 70 Contact: :612xxxx1250@XXX.XXX.XXX.97:5060> To: :04xxxx789@XXX.XXX.XXX.38:5060> From: "088xxxx200" :612xxxx1250@XXX.XXX.XXX.38:5060>;tag=3f476535 Call-ID: 3W2WdsvYbZ8fUwyD5FCsew.. CSeq: 1 INVITE Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REGISTER, SUBSCRIBE, NOTIFY, REFER, INFO, MESSAGE Supported: replaces User-Agent: 3CXPhoneSystem 15.0.62928.5 (62293) Replaces: q29PgDu3f7tCSCKxCqI5gg..;to-tag=7vK2BgvU22D7S;from-tag=0640c502 P-Preferred-Identity: :6123xxxx250@XXX.XXX.XXX.38:5060> Remote-Party-ID: "6123xxxx250" :6123xxxx250@XXX.XXX.XXX.38:5060>;party=calling Content-Length: 0 SIP/2.0 480 Temporarily Unavailable Via: SIP/2.0/UDP XXX.XXX.XXX.97:5060;branch=z9hG4bK-524287-1--- 9a4d0b17e47a392c;rport=5060 Max-Forwards: 70 From: "08xxxx0200" :61xxxx1250@XXX.XXX.XXX.38:5060>;tag=3f476535 To: :0xxxx6789@XXX.XXX.XXX.38:5060>;tag=NUNX4a8ctZ5cc Call-ID: 3W2WdsvYbZ8fUwyD5FCsew.. CSeq: 2 INVITE User-Agent: SBC-Summit Accept: application/sdp Allow: INVITE, ACK, BYE, CANCEL, OPTIONS, MESSAGE, INFO, UPDATE, REGISTER, REFER, NOTIFY Supported: timer, path, replaces Allow-Events: talk, hold, conference, refer Reason: Q.850;cause=96;text="MANDATORY_IE_MISSING" Content-Length: 0 P-Asserted-Identity: "61xxxx6789" xxxx6789@XXX.XXX.XXX.38 Dave P.