I just got back from a multinational trip: Canada, German, Japan. The coverage was pretty reliable, albeit slow. I'd assume it was around Edge speeds and left something to be desired. It's good enough to check email and map directions. Although, I'd be sure to have the map downloaded before hand. The GPS functionality came in very handy.

With every country visit, T-mobile would send me a text welcoming me and telling me to buy up to Global Data plan. You don't need to and data worked fine. Just be sure to enable data roaming in your phone settings.