Here is the scoop on international SIM cards. If you are traveling only to one country, it makes sense to get a "country specific" SIM card as the rates are very low. For example, the Lebara SIM card for Australia gives you rates of $0.05 to call the US plus free incoming. However, if you are traveling to many countries - or even just 2-3, get a roaming SIM card. I use the National Geographic SIM card for this. Often, I am in a country for 2-3 weeks at a time and I use a local SIM card. The last one was the Uno Mobile SIM card for Italy. You can get in on Amazon or Cellular Abroad - International Cell Phone Rentals and SIM Cards, a company that specializes in country specific SIM cards and will talk to you on the phone, something that Amazon will not do.
Personally, I would never roam with my T-Mobile. I do not want to pay a buck a minute in Europe for a call, especially from Aunt Ruth who won't shut up! "Oh, you're in Italy? that's nice dear...tell me about it!"