The monetary sticking point would be, well, what handsetsubsidy (to be recouped through monthly charges on say two year contracts) is China Mobile willing to offer those who buy iPhones.
But most people look for a handsetsubsidy: a lower upfront cost for getting the phone in return for paying some set fee per month over the life of the contract.
The key issue is money, and the fact that Apple prefers to take larger cuts of subsidy payments from mobile networks, compared to other handset makers.