I've had T-Mobile and wasn't happy with the service. That being said, it was with the 1st generation Treo 180. I've had Sprint (with Treo 300) and it was quite good. I had zero complaints.
That's my 2 cents. For what it's worth, I'm with Cingular now. Overall, their service is solid. I have to say that I preferred Sprint, but not by much.
Chris |