I have always recommended grabbing a local SIM for your phone when traveling abroad. It gives you a local number, cheaper calls and usually access to data on your smartphone. Google Maps can save your life when you are wandering around a cobblestoned downtown in Europe, but only if you have a data connection.
T-Mobile has decided to change the rules on that process. They now offer data for your phone in a pile of countries worldwide when you have one of their Simple plans.
Free data, free texting and international calls for twenty cents a minute on top of already having the most competitive plan pricing of all the major carriers makes this really appealing if you have call to travel abroad. Couple that with the fact that they DO NOT REQUIRE A CONTRACT, and it may make more sense to sign up for a TMobile plan before you go on your next trip and cancel it when you get back home.
Keep in mind that you will have to have an unlocked, Quad band phone to get the full benefit of this. I would personally recommend the new Google Nexus 5 but any unlocked phone will do.
TMobile claims that they are trying to be different than any other carrier and if this any indication than zigging rather than zagging is working for them.