I have been using a ATT Pre 3 on T Mo for about 3 weeks. 2 weeks in the EU. T Mo uses 2g for the "unlimited world data." Of course, T Mo sells better/faster service for extra $$ when you get overseas ;-)
Is good for emails and texts.
text with a photo did not work.
GPS pretty bad - worked once in France, once in Germany, and has not worked in the US yet. Tried rebooting, GPS fix, #*477#, etc. etc. with no luck. When GPS did work map loading was essentially unusable with 2g.
Basic browsing was OK with patience..........i.e. if you really need the info you'll wait otherwise your searching for a wifi connection.
Calls on T Mo are OK. Sprint seems to have better reception overall.
Nonetheless, using the Pre 3 is great, even with the draw backs.
I'll put my Pre- to sleep on Sprint for a couple of months while I travel and add an update in a few weeks.
Don't forget to put your sprint phone on call forward busy no answer. That's the free one.
But now that you're using it in another country can't you get a prepaid sim that offers HSPA+ on any of the Pre3's bands? To heck with only 2g on t-mo. That's why i gave up on that method and am still on sprint too