Which phone to choose?

My uncle had spice d-88 duel sim mobile but from few months its keypad has been acting weird, keys stops working sometimes.
So he wants a new phone, which should have, gsm, 3g, big screen and he is saying something about it should work globally, not the sim but the mobile is it so? that we need a different mobile for different countries?
He is thinking about a black berry phone, i think iphone is also good choice, any suggestions?
Price limit around 15-20k