Unlocked iphone from att, can I use it in hongkong/china?

I'm going to get my iphone from att unlocked by them. After they unlock it, can I use it in china? How? Do I just by those sim cards and enter the number into the phone? Viola?

Yes it will work if you unlocked means it can be used as per your wish at anytime and any place in the world

Yes you can use it any where in world with any sim card bcos its unlocked

Yes, you can use the AT&T iPhone in China if unlocked.

Yes, worldwide as long as it is the same network type (GSM/CDMA)

Yes you can use it. Once an iPhone is unlocked, you are free to insert any SIM card or use it with any compatible network. In having an unlock iPhone, you are able to use local SIM cards and for frequent international flyer like you, having an unlocked iPhone is definitely cost-effective.