does facetime use airtime minutes or data usage?

FaceTime uses neither airtime nor data as it works only over WiFi. I believe the previous poster means that, if you make a call and then transfer to Facetime, through the call, the original call will use airtime. However, as you can make a Facetime all using the button in the Contacts, you don't have to make a voice call first or use any airtime.

Facetime currently works on wifi only and therefore no data usage. However, it will incur airtime during the call.