Its not like in India, the person will have to break the contract or else pay the fees monthly.
Anyways since you asked, yes the iPhone 3G is unlockable. But if its on latest firmware (3.1.3), then there is no unlock option for now. It may be unlocked in future, when new tools comes out.
If the person in US is buying a new iPhone 3G or 3GS, then it'll be on latest firmware and you won't be able to unlock, atleast for now