Honestly, I'm not even sure I'm going to stick with T-Mobile after their announcement that they will cap data roaming at 50 MB per month, and once you reach that, you can no longer use data whilst roaming. This won't work at all for me because usually when I roam, I'm out for weeks at a time and can hit 50 MB pretty quickly.

Noting that you have a Turkish football crest in your avatar, this may be a sticking point for you too.