Help in Choosing PDA/Handheld and Carrier

I am considering a Blackberry to check e mails, and send text messages,
rarely, when I am away from my PC or laptop. I also need to be able to
tether my laptop on a rare occasion when I am out of the area without a
hook-up.
I have a voice plan with Cingular but their data plans seem to be a bit more
costly than the other carriers. I don't mind having two devices. I think
T-Mobile is the lowest in price but what about their coverage. I am also
looking at who gives the best discounts on their equipment. I have been
looking at the 8700 series of Blackberry's. It appears to have the most
advanced technology as opposed to the Q or a couple of others. I am in
Georgia but travel to other states at times. I have heard that Verizon is
the best way to go. Any advice would be appreciated.