I got a Blackberry a few months ago for work. Amazon supports the enterprise server and besides getting my work email and calendaring, memos, and full outlook integration, I can also surf the company intranet and use a variety of web-based tools to keep monitor things and understand issues as they are developing. This is very very cool.
I've also started using the blackberry for other things, like shopping lists. It's nicer than pen & paper because as I pick up things, I delete them from my list and it gets shorter. That's much easier to see what is left plus it makes me feel good to have my list get shorter.
What dawned on me today while adding some things to the list after talking to my wife was that I was able to add those things one-handed. I didn't need to break out some stylus to tappity-tap the additions to the list.
The iPhone has a touch screen but it is configured for fingers -- no stylus. Blackberry has a full keyboard and the great trackball -- no stylus. Palm -- the PDA of yesterday -- stylus. Windows mobile phones? Stylus. Blackberry's next big release? Touchscreen ala iPhone. iPhone's next rumored big release? Full keyboard ala Blackberry. The top two convergence phones don't use the stylus.
Nintendo DS uses a style and is well received for it. In fact, I do my best to only buy games for the DS that use the style because it makes gaming so much better. My HP laptop is a convertible touch pad device and the touch-screen / pen is really nice for certain things.
Both of those uses are things that require your full attention and you expect to have to use both your hands. Your Phone / PDA is really an accessory. You use that briefly while doing other things. It is not expected to always be an all enveloping experience and along with that, you don't expect to need two hands to use it.