I haven't used GPRS, but I have been gearing up to look into it as well. Here is what I do know:

Verizon offers essentially what is a Cellular Broadband Connection. I know others who use this service and have told me it is very good, except it is only availble for use in major markets at the time. Its a good broadband connection from what I have seen.

I also have seen stormchasers using satelite or cellular connection cards for internet to access weather information and maps, and knowing that many of the areas they cover are places where cows outnumber humans and corn outnumbers all, so they aren't a major market. They seem to work very well.

Depending on what areas you're going to, the Verizon wireless broadband might be a good choice, but I know there are dashboarders on here that use some of the other ones, and I too am interested in hearing their suggestions.

-Brad