I have Alltel data service as I live in a rural area where the only alternatives are 24-36Kbps dialup or 400-700k satellite. I pay about $60 per month and Alltel is "unlimited," however with the Verizon takeover I'm not sure how this will affect things. I typically get speeds between 400-800Kbps, but have gotten up to 1Mbps on occasion. If you want more information about the various services look at www.evdoforums.com. Note that like any wireless technology, the total bandwidth at the tower is shared by all clients and as more people use the service, the speeds go down.
Personally, I can't wait to move and get cable or DSL.