Yesterday we reported on why JailBreakMe would be worth your time. Today there is another cool feature that you only get on a jailbroken iPhone 4 - FaceTime video conferencing over 3G.
9 to 5 Mac has tested it and published the instructions. You can watch their 3G FaceTime call test below.
9 to 5 Mac also measured the amount of data a 5 minute FaceTime call uses. We are looking at 15MB of data. This explains why carriers do not want Apple to enable FaceTime over 3G yet. 3MB per minute is a lot. I assume we will have to wait for 4G to get cellular network based video conferencing on the iPhone.
See also the Fring App for 3G FaceTime calling.