What does an iphone need in order to work in another country?

I'm sending an iphone 4s to brazil to a cousin and want to know if it will work there. Does it need to be unlocked or will an iphone with a clean esn work? Please let me know soon!

If your cousin needs to use the iPhone with a Brazilian SIM card, Then the iPhone must be unlocked. There are various methods to unlock an iPhone. One among them is the remote unlocking service. This method of unlocking is safe, simple, affordable and quick. You can get the remote unlocking service for an iPhone 4S from http://www.unlocking4u.com/apple-iphone-4s/rs16wp9/ at low cost with easy unlocking instructions. This method of unlocking doesn't require a jailbreak too. All the best mate.

An unlocked iPhone works anywhere with any simcards, but a locked one can works only with its network locked to. For example, if you buy a locked iPhone in the US that is locked to AT&T network, your cousin can't use any local brazilian simcards. He has to use AT&T simcards and pay extra money for roomming service.
i think you can buy a locked iPhone and unlock it through unlocker websites. My friend used 1 of them for unlocking his iphone for just $25 in 24 hours.their unlock was official apple unlock and done through apple. They just got my friend iPhone imei # and unlocked it. They support iphone 3G / 3Gs / 4 / 4s /5 and ios 6 too.
check their website:
http://officialappleunlocker.com/