Any device that registers as a 3rd party device will only get basic features. FAC requires a specific interaction with UCM that most likely will not appear in phones that register as 3rd party. Since these phones do not go through a rigorous test cycle with UCM, and no specific development was done to accomodate these types of features, it is not surprising that this will work.
Bottom line, using SPA phones with UCM gives you basic phone operation. If you want advanced features like FAC, you need to use a CISCO phone that has been designed from the ground up to work with UCM.
