Here's a pro-tip. If you want to be the world's largest smartphone maker, you should probably cut a deal with the world's largest wireless carrier. It sounds simple. But if you're one of China Mobile's 700 million subscribers, you still can't buy an iPhone on contract. There are two reasons for this. First, China Mobile's current 3G network is a custom job. And that means Apple would first need to create a modified iPhone to work with it at full speed. That may become a non-issue though.