I have a 930 that I have been using on AT&T. I have no trouble making/receiving calls, receiving or sending texts, or using MMS. That all works fine.
The trouble I do seem to encounter is on the data side. The data technically works, but it's spotty. Sometimes it is horrendously slow, and other times is perfectly fine. And this happens when I'm in the same location. I attribute it to the phone having trouble locking onto a signal correctly... but I could be wrong.
I notice it's constantly bouncing from H to H+. Not sure what that means or how to avoid it? I love the phone though and most times I'm on WiFi so I don't really notice the data issue...