HandSpring Treo
I use the handspring treo 180. If you like the Palm OS, I think it is the best combination out there. The keyboard version is fantastic. I've used the Palm since 1995 and would never go back to Graffiti.
Its a great device but the phone software integration is still in its first iteration. Its decent but is not phenomenal. Given HandSpring's track record I would expect it to get better.
The functioning of the device is a bit slow. For example, if you punch in a speed-dial number there is a noticeable delay of several seconds before the call is initiated.
But these are minor quibbles. All in all, its been a great device to have. If you find that you're always carrying a palm and a phone, you may like it.
If I could provide some advice, get the color version (Treo 270 or Treo 300). The 180's screen is a bit dim; like a throwback to the palm3 or earlier monochrome editions.
Hope this helps