The T616 would be good for testing here, but keep in mind it is still a tri-band phone that lacks 900mhz. So, it will be less then perfect if you use it in Europe.

I think that is T-Mobile's issue with 850. AT&T pushed ahead with it, instead of trying 900 GSM here, something almost every GSM phone supports. T-Mobile on the other hand has lots of international customers to worry about, and until common replacements across the board are quadband, they need to keep the majority of their user base happy. I think if it was still Voicestream, they would have gone 850 as well.