Site getting Authentication required error when trying to add a new Cisco phone
There is an integration doc titled Device Integration Manual Cisco Systems Unified Call Manager
This covers most of the requirements.
Firmware on the Cisco phone should be 1.4.8 with V02 or V05 hardware version.
Also... in the CUCM administration GUI.... Not only does the device need to be added to the Fusion End User, it also needs to be added to the Fusion Application User.