T-Mobile has a pretty good add-on for international roaming. I dont think they charge extra (at least not expensive), but you do have to request it. A lot of Europe is 99 cents (US) per minute. The thing I like about it is (assuming I understand it correctly and Im pretty sure I do) is that the rate you get while in a country doesnt change no matter where you call. So if you are in Germany, it cost 99 cpm to call US and 99 cpm to call Argentina.

More expensive than a local SIM but a lot more convenient.

http://www.t-mobile.com/Internationa..._RoamWorldwide