Just like in Europe. It's the same normal international data plan for most carriers (I've done it on At&t and Verizon).
And you get cash from 7-11 (yes I'm serious). American cards very very frequently don't work. Especially in any sort of machine, particularly vending machines and the train ticket machines. Many atm's won't take american cards either. But, every single 7-11 (which are everywhere) has an atm which takes american cards. They sometimes say 7-i, or Seven and i holdings. It's all the same thing (7-11 is actually a japanese company, and they are everywhere). Other than 7-11, every Post office should have an ATM that works too, but they are way less common.