Treos are notorious for being buggy, unstable, and spontaneously rebooting or requiring frequent reboots.
I had a Treo 600 from Cingular and I can speak for that firsthand. During the course of the day, it must have rebooted at least 5 times -- many times in the middle of a call.
I won't speak for others, but I won't tolerate a smartphone that behaves like Windows 2.0. A smartphone must be stable -- like an alarm clock, TV, etc.
I sent it back to Palm and went to a Blackberry. No stability problems and it just flat out worked.