Very nice and useful article.
One interesting point in comments: FaceTime can also be voice only:
“kem said 8:28PM on 8-06-2010
A lot of people are not aware of the fact that FaceTime also works without video. You don’t have to stop the FaceTime call and call the other person back if you don’t want video (anymore). Just press the Home button during a FaceTime call and you got yourself a high quality audio-only VoIP call that doesn’t use up your cell phone minutes and uses less bandwidth than a video-enabled FaceTime call.”