A couple of random observations:
1) China Mobile has lots of GSM users, but a totally unique 3G system. Apple would have to either only sell an EDGE phone (is there EDGE support in China at all?) or create a unique iPhone model for them.
Nokia, HTC and Palm are supposedly planning China Mobile 3G models, btw.
2) China Unicom only has about 140 million GSM users. The USA has that many CDMA users and they have far more money for data plans such as the iPhone needs.