The warning message, originally snapped by Romanian site iDevice, apparently pops up when you try to turn off 3G while on a FaceTime call. The missive reads, "Disabling 3G will end FaceTime. Are you sure you want to disable 3G?"
Currently FaceTime only works over a Wi-Fi connection, so there's no reason that switching 3G on or off should affect your video chinwag. But the message -- present in the recently released iOS version 5.1.1 -- has led to speculation that Apple is poised to turn on FaceTime for 3G.
I've tested switching off 3G during a FaceTime call, and can verify the pop-up does make an appearance. Turning off 3G didn't end the FaceTime call though, despite the warning.
There doesn't seem to be any reason why FaceTime wouldn't work over a 3G connection, but the quality of the video calls could take a hit. Apple's not keen on exposing its customers to a potentially less-than-perfect experience, preferring to limit the functions of its gadgets rather than risk something being a bit broken.
It's fair to say that FaceTime hasn't really taken off yet -- mostly due to the unflattering angles that front-facing cameras lend themselves to. Would Apple's video-calling feature be more popular if it worked over 3G? Let me know in the comments or on our Facebook wall.