Well I have had the pleasure (

) of owning the Z5600 and a Pretec CF GPRS card (which was a pain in the butt to get working right) and was able to get it to use my AT&T Wireless (now Cingular) EDGE service.
Then I switched over to Cingular and bought the Nokia 6230. It has bluetooth. Paired with a Socket Bluetooth CF adapter and you're ready to go no matter what Z you have. I've used it on the Z6K and the C3K and it works great.
The best speed I've ever gotten from the EDGE service was in Tallahassee, Florida where my speed topped out at a respectable 23K per second download. I'm in Phoenix, AZ right now and I usually don't get anything better than 7 or 8K/s. Lag time yeah, yeah... it lags real good.
My phone stays in my holster. Have it paired with the Z and have auto-connect set so it never bothers me. I just turn on the Z3K and hit NetFront (need to get a better browser agh...) and it connects right off. Nice.
I know they have UMTS here in Phoenix but right now I don't have a phone that supports it so... mebbe I'll have to check out that 6630 and twist the arm of the guy at the Cingular store to let me upgrade without charging me extra since they sooo kindly sold me a fone WITHOUT UMTS when they knew that I'd probably want that instead *grumble*. Anyhoo just my 2cents.