At the moment official Apple HK version of the iPhone 4 through authorized Apple resellers are still non-existence. It will probably not change until Apple HK online store change their "estimate ship" date to 24 hours for the iPhone 4.
As for warranty, Apple will most likely not exercise their option to ask the warranty holder to return the iPhone 4 to the place of purchase, if you live in a country where the iPhone 4 is officially available.