I've found that most professionals don't like being "available" during off work hours. The exception are workaholics and those who are self-employed.
Some even have two cell phones.
So, if your work has you on the road, or frequently in a situation where access to a computer and the internet is limited - a phone/pda will probably increase your productivity. However, if you almost always have access to email while working, you'll probably rarely use the pda features, and if you don't use it often enough - you'll probably discover that after the initial usage, you'll never use it again.
I have the 24 CTU Ringtone I can email ya, for your new gadget. I don't have a clue as to what a PDA, or a Smart Phone/Blackberry Plunge even is.
(;^0)