Take a look at the BlackBerries as well. The 8700 series offers a good compromise between size and functionality. It's thinner than the Treo, but a smidge wider. I feel the BB's keyboard is superior. The screen is gorgeous, and the device is very rugged . . . although still quite a bit lighter than the Treos. The CDMA-based 8703e I use on Verizon offers excellent reception and voice quality. There are other models in the 8700 line that will work with your selected carrier.

While it doesn't have anything like the same number of 3rd party apps as the Treo, that's also a blessing . . . virtually no software conflicts; the BB is rock-solid and will never reboot itself in the middle of an important call. It's included email handling is superior to both Palm's and WM's, whether MS Exchange is involved or not (although, to be fair, you need RIM's BES to integrate with Exchange).

None of the current offerings other than the 8100/Pearl offer cameras or memory expansion, so if you want to do anything besides get your work done reliably the BB may not be your best choice. But it's worked out very well for me.