Apple’s open source (albeit with the source code yet to be released by Apple) video chat spec first launched in 2010 with a vague promise from then-CEO Steve Jobs that it might be available over cellular data connections once the cell networks “get ready for the future.” Since then, there have been plenty of rumors that the iPhone would soon gain the ability to make FaceTime calls over 3G—particularly as the launch of iOS 5 loomed last October—but it still hasn’t happened. Attempting to make a FaceTime call when not connected to a WiFi network results in a pop-up that explains a WiFi network is necessary to complete the action.

via Despite higher network speeds, no FaceTime calls over LTE.

I wonder why FaceTime cares what network carries its data.  The network layers should be independent of the application.  If it works with WiFi it should work with LTE.