I had a palm treo 600 for several years with AT&T, and didn’t have any trouble with it at all. Went through a few batteries, but that’s normal with any phone. It was a perfectly fine smartphone.
Switched to an iPhone last year, but I’m looking forward to the new Windows Phone 7 Series due out later this year.
Back in the day I LOVED my treo 600. It did crap out on me though by getting just a few droplets of water on the touchscreen.
My replacement phone had windows OS, I liked the OS but not the phone.
The newer Treo’s that have windows would have probably been the ticket.