I have gotten mixed results with my Treo 650. It's great for email, and the Palm OS PDA is unbeatable. When I was in Europe I updated this blog from the Treo every day.
But(!), I can't leave the phone on for more than an hour or the whole thing freezes and I have to reboot it. Rebooting involves taking the cover off, removing the battery cover and poking the stylus in a little hole next to the battery... no fun.
So, today I gave up. I bought a cheapo phone that I can use with the same Cingular chip, which means it's the same Cingular account. This phone appears to work (a Nokia 6010).
My goal of having just one electronic gadget that is both phone and PDA is a failure! Maybe PalmOne will release a fix later that will let the phone work, but I'm not holding my breath.