It depends on the country or countries. In many parts of the world, they use GSM (Global System for Mobile Communications) signal for cell phone while the US does not. Cell phone sold here in the USA may or may not be usable at other country. Check the destination country first to see what type of signal or how many Hz they use.
It's a safe bet for your friend's daughter to buy a phone and calling plan at the foreign country she's staying. It's usually cheaper and you know for sure that the phone will work. If your friend do decide to buy, make sure she buys the right phone (the signal we talked about) and one that is unlocked, meaning it can work with SIM card from any phone company. I have friends who bought GSM unlocked phone here, go overseas and buy new SIM cards there. But it all depends on the country. Hope it helps.
P.S.: I didn't realize this thread was posted back in April...