Questions:
1) Where can we buy iPhone 4 without any contract?
Maxis and Digi do sell. but because no stock, so they only sell it with contract. The easiest way is Singapore Apple online store.

2) Do we need to jailbreak or unlock the iPhone so that it can used in other China Telco?
China have some restriction on their wifi frequency or smth like that. so even u get an official unlock set from china, there are still difference in it.

3) Can we unlock the iPhone without jailbreak? If yes, how?
any unlock or jailbreak phone that u do on your own will void ur warranty. so if u want to unlock it urself, why not jailbreak it as well since the warranty already void.