I can't find documentation to prove this but I believe this won't work the way you want. The mechanism that Cisco IP phones use to communicate CFA information is a proprietary SIP extension, which is blocked on third-party SIP device types. In other words, RFC3261 doesn't provide a mechanism to do this. Most likely, the way the phone deals with CFA is to issue a REFER when it receives the INVITE from CUCM. The easiest way to be sure is to just grab a packet capture of both the user enabling CFA and an incoming call while it's on. If it does in fact use REFER, you need to set the Rerouting Calling Search Space on the device in CUCM to a CSS that includes whatever destinations CFA should be allowed to reach.

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