Thanks guys! I appreciate all the input.
I bought my iPhone4 here outright, direct from Apple with no contract, so no problems there. I could always tell my carrier that I'll be in the USA, but they charge like crazy for global roaming and I get tons of work calls on this cell - I'd rather not when the time zone is ~7hrs different, to be honest.
The Simple Mobile or GoPhone might be the way to go. I'll check it out, but it looks like I could just put it in my handset.