Me and my husband just recently bought Iphone 4 and I just want to share my experience ;-)
After asking to many friends and made several survey about IPhone 4, we found out that there are 3 kinds of IPhone 4 in china :
1. The chinese one : It has CH code in it`s Part No. (E.g Part No. MC763CH/A). They are locked and also have problem on its maps application. Please read article about the chinese IPhone 4 maps before you decide to buy it. It`s a big issue, especially for foreigners since you will only find the chinese name of the street in abroad.
2. The US one : It has ZN code in it`s Part No. (E.g Part No. MC763ZN/A). Can`t be upgraded, it will hang and crash ones you try to upgrade (happen to many of my friends)
3. The Hongkong one : It has ZP code in it`s Part No. (E.g Part No. MC763ZP/A). Around Protected content more expensive than the chinese one (we bought two 16 GB IPhone 4 for Protected content but it`s perfect. Can be upgraded, use google maps application, chinese character and unlocked.
FYI, if you go to apple shop, they only sell the chinese one with china unicom provider.
OK, Hope this information help you guys.