Many people are curious to know how much data FaceTime over 3G actually uses. We put two iPhone 4s to the test, one running FaceTime over 3G, and took before and after screenshots of the data. As you will see, if you do the math, a 5 minute FaceTime call with lots of movement used 14.7 MB of data. — That’s about 3 MB per minute.
Before 3G FaceTime Call
After 3G FaceTime Call