The 3GVenice plist trick doesn't work on my ATT 4s on IOS 6.1. It worked on IOS 5.1.1, though. If I try to use FaceTime over 3G, it says I don't have a network connection and takes me to Settings -> General -> Cellular. There is a new setting there for "Use Cellular Data for FaceTime" but it won't let me turn it on. It says I don't have an eligible cellular plan.