I just heard from a friend (who I'm almost certain is using T-Mobile with a new set of iPhones 5s) that she saw a significant extra charge on her most recent cell bill due to FaceTime usage. I haven't actually seen the bill, but this has me entirely confused. So far as I understand, FaceTime uses data, period. If it's Wifi, it has nothing to do with carriers. If it's over the cellular network, carriers could disable it entirely (at least in the past--can they anymore?), but if it's enabled, FaceTime data is exactly the same as any other data. So long as you don't go over your data limit or incur roaming charges, it should cost nothing. And since T-Mobile doesn't have overage charges, they just throttle, it should be impossible to rack up extra charges unless you have data roaming turned on and were roaming when using it. Am I wrong about this? Is there some fine print I've never heard of? I know I've used FaceTime video on T-Mobile's network with my own iPhone and the only extra charge I've ever had was when I accidentally made an international phone call to someone in Canada without recognizing the area code as non-US. I'm certainly going to ask to see her bill so I can figure out what's up.