Blackberry's are very very nice (when they are working right)
Frequent lockups and non delivery of mail
Expensive
flacky due to all the stuff they have to integrate to
Cell models even have issues.
I would go with a Laptop if that is all you get.
Sony Vaio- smallest model, so you get all the Win/Net functionality and a usable screen space.
PDA's and Blackberries are secondary to a real workstation for use when you are away from your desk.