Mobility and dancing bears
Size is the problem.
Cell phones are small. In fact with the current generation of phones they are too small - at least in the keyboard. Unless you are a kid or a skinny Asian female the size and placing of the buttons on the phone is a lot smaller than your fingers. This is just bad design.
(Why is it the very latest cellphone/gadgets are usually shown with skinny Asian females? ... oh nevermind).
For talking cellphones are great. For sending short text messages (I have a teenager) cellphones are - a bit of a pain but tolerable. For web access - between the tiny screen and tiny keyboard - cellphones are a dancing bear.
"The wonderful thing about a dancing bear is not how well he dances, but that he dances at all."
My new cellphone has a (lousy) builtin camera, with truly brain-dead supporting software/GUI in the phone, and an uninspiring picture gallery at the phone company site. Dancing bear time again.
No, I don't have a PDA or cellphone/PDA hybrid. Ever see the George Carlin routine about different versions of "stuff"? PDAs are little limited computers with small screens and way-too-small keyboards. One friend is on - I dunno - his sixth(?) PDA. Seems to be more of a hobby than a useful tool.
Cellphones are great for talking. Bluetooth to a wireless headset sounds pretty nice, though with my latest cellphone has a "speakerphone" mode, I have almost stopped using headsets. Flat-rate high-speed connection to the Internet via bluetooth to my notebook sounds like a killer app - if you can talk at the same time.
I will take usable and useful over whizzy every time :).