unlock question

[burntmushu]

hello. i got a question. my father spends half his time here in the states and half the time in korea. i know if you bring a unlocked phone you need to pay telecommunications $300 to register your phone frequency or you won't be getting any single unless you're roaming so everything will be international. so here's my question. where to purchase the iphone? would it be better for me to purchase the iphone in korea and be able to pop a att sim and use it here? i heard only att brands the iphone and other carriers are unlocked. or would it be better to get 3gs and get it unlocked and pay for the frequency link? and if so which firmware or firmware should be avoided due to no unlock is available for the 3gs? thank you.