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.