A user reports that when receiving an inbound call on their IP Phone from the PSTN they are unable to transfer this call to another PSTN number. What is the reason for this failures?
A. The IP phone is configured with the wrong region.
B. The incoming calling search space of the SIP trunk does not include the partition of the line in the IP phone.
C. The service parameter related to Offnet to Offnet Call Transfer is set to TRUE.
D. The gateway is configured with the wrong device pool.
D is indeed correct as detailed in this article: https://www.cisco.com/en/US/docs/voice_ip_comm/cucm/admin/4_1_3/ccmfeat/fsxfer.html#wp1048448
Wish someone would fact check these things.
Edit to my post, I fat fingered D instead of the actual correct answer of C.
C is correct answer