One of my first PDAs was an HP (Compaq at the time) iPaq. It was a revolutionary device, but it wasn't a smartphone. It ran Windows Mobile (Pocket PC at the time) and it was considered a "state of the art" piece of technology.
Today, we live with so many smartphone options. My wife and I both used to have a Palm Treo and I still see that many health care professionals are using the Treo. Well, if you like the Treo form factor (touch screen plus QWERTY keyboard in a "candybar" model), then you may also like the HP iPaq Glisten on AT&T. This 3G smartphone runs Windows Mobile and it resembles a BlackBerry. However, the touch screen feature makes it easy to navigate on this device.
If you're a former BlackBerry user and if you're switching to Windows Mobile, this may be the device for you.