I have a CUCM 7.1(3) and Unity Connection 7 deployment with two PSTN connections, 1 SIP and 1 PRI. When calls come in over SIP to an AA, and someone selects an option to XFER to a CUCM Hunt Pilot, the caller on the PSTN hears constant RingBack. The phone(s) in the Hunt Pilot's LG ring normally and all other call processing appears normal. If I call a DID on the PRI which is pointed to the same AA, and XFER to the same Hunt Pilot, Ring back is normal. Normal rining is also heard when I call the AA from the inside and Xfer.
Also, If I change the UC AutoAttendants XFER to Supervised Transfer, the caller on the PSTN hears one ring back and then silence.
Any ideas? It does seem SIP related.
Found exactly like: http://tools.cisco.com/Support/BugToolKit/search/getBugDetails.do?method=fetchBugDetails&bugId=CSCth05703 this only happens with blind transferes not supervised as you've already seen.