<p style="text-align: center;">Before</p><p style="text-align: center;">After</p>
The folks at 9to5mac has tested the iPhone 4 Facetime over the 3G network and according to them, 5 minute FaceTime call with lots of movement used 14.7 MB of data (that means 3MB data / min)
[Via]
<a href="http://dailyiphoneblog.com/2010/08/04/facetime-over-3g-use-3mb-data-min/">

[Read the original blog post]
</a>