Looks like iOS 5 has lots of hidden features. Recently we’ve seen how one can enable both the hidden Panorama camera mode and the autocorrect band for keyboard in Apple’s latest mobile platform and now the tweakers among you can enable FaceTime over 3G.
With the proper warning, you can tweak to make this available: you’ll need iFile (which you can grab from Cydia) with which you’ll open N90AP.plist found in /System/Library/CoreServices/SpringBoard.app/. For full instruction, head over to the source link to see what it is that you have to edit and add to the file. That’s all you need to do and you can hopefully make FaceTime video calls over 3G.