It would only seem to make sense, as FaceTime video calling can only run over WiFi at the present time, but the questions had still been raised. Apparently the option exists for a caller to flip from a voice call over to a FaceTime call without any sort of break or transition. So if that happened, the query was whether or not your minutes would continue to tick.
Silicon Alley Insider got the quote from the bite of the Apple:
“The voice call ends as soon as the FaceTime call connects. The FaceTime call is over Wi-Fi so does not use carrier minutes.”
The question, of course, will rise again once the carriers are prepared for FaceTime traffic. Given that the next version of FaceTime will also work over 3G, an entirely different approach toward billing will need to be taken in order to keep everything on the straight and narrow.