Considering that we already know Face Time is a WiFi only video calling platform, it seemed simple enough at first glance that a Face Time call would not use your voice minutes. Many still wanted official confirmation and that confirmation has now come from Apple.
Apple has announced that Face Time calls that are initiated within a voice call will not count against your call allotment. The voice call is terminated as soon as the Face Time call is connected. If you think about it, even if Face Time calls do count against your voice plan minutes, since AT&T is the only carrier for the iPhone in the US and calls between AT&T users don't use minutes this really doesn’t matter.
I guess this is nice to know if you have friends in the UK or Canada who are using Face Time on another carrier. Apparently how exactly Face Time calls over 3G, reportedly on the list for the next update, will be charged is under debate. I bet you get double hit for data and voice usage in that instance.