Its been possible thanks to a jailbreak tweak for some time -- so we knew it worked -- but Apple still hasnt given FaceTime the blessing to work over 3G. But now it looks like Apple is about to let users FaceTime over 3G (or 4G), though, with an error message giving away the secret.
The message (pictured above) is new to iOS 5.1, and has only been discovered for the first time this week, despite iOS 5.1 being out for a few weeks now.
The Verge reports that if you try to disable 3G whilst on a FaceTime call, the iPhone will show an error that warns; "Disabling 3G may end FaceTime. Are you sure you want to disable 3G?" Right now, pressing disable does nothing, because calls only work over WiFi. Additionally, if you enable 3G again whilst on a call, it warns "Enabling 3G will end your phone call. Are you sure you want to enable 3G?"
Back in 2010, when FaceTime was announced, Steve Jobs stated "[Apple] needs to work a little bit with the cellular providers to get ready for the future." It seems like that future is now, and that could be an iPhone with 4G LTE.
With WWDC now under two weeks away, it seems like Apple is about to flip the switch and let users FaceTime regardless of connection type.