With Sprint or Verizon, when you don't have EVDO you'll have 1xRTT which isn't dialup slow but isn't that fast. It's ISDN speed or thereabouts and you'll get 80-120Kbps throughput with it. It's enough to be functional. Too bad Cingular doesn't have a nationwide UMTS footprint. Theirs is the fastest 3G service I've used. 1200Kbps sustained transfer this past weekend in Dallas. I literally felt as though I was on a decent DSL line and for wireless, that says a LOT.

I'd initially said that Verizon likely had a larger EVDO area but that's not true at all. I hadn't looked lately. Sprint has leapfrogged Verizon (at least in this area) and has MUCH more EVDO coverage. That's a good thing as I prefer Sprint for data services (I have both EVDO cards). Sprint has recently instituted data roaming so when she's NOT on native sprint coverage she should still be able to roam and use data if the carrier supports 1xEVDO/1xRTT. You'll need to talk to Sprint to find out how much that'll cost though! It also works in Canada.

Here's Sprint's info page on where they have EVDO coverage.

Here's Verizon's coverage locator.