A:AnswerIf you buy the AT&T phone, you will be qualified for the plan because you didn't buy an unlocked phone(That's what unlocked phone exclusion means). What you do after you get the phone is your own business, but AT&T won't unlock he phone right away, unless you pay off the full price of the phone first. If you don't pay off the phone, it will be blacklisted and may make it difficult to use later on.
A:AnswerIf you buy one with an AT&T contract, you just switched to AT&T. I would look for an unlocked one, this way you can use it with any carrier you choose. You can also buy one that is still locked to a specific carrier and pay to have it unlocked for use with MetroPCS. I would suggest switching to AT&T though, I had MetroPCS before and their coverage not nearly as good as AT&T.
A:AnswerI would suggest buying an unlocked Samsung Galaxy S7 for your friend to use on a carrier down there. If you buy one locked to a carrier in the USA, it will have to be bought on a plan here, and you will be paying for additional coverage outside of the country. It isn't worth it.