Had an opportunity to do a direct comparison this past summer between AT&T and Verizon for wireless cellular data when taking a three-week sojourn out west from Indiana to the Tetons, then to Yellowstone, and finally the Black Hills on our way back home. We had two iPhones on a Verizon data plan, and an iPad on an AT&T data plan. While we did run into locations where we didn't have service from either provider, most notably in Yellowstone, there were many times we had to use the WIFI hotspot service on an iPhone to connect to our iPad as there was no AT&T data service. This was necessary for us as our iPad was hosting our travel applications, including Allstay, iExit, etc. Having said this, I expect that there would be fewer incidence of that happening out east where both carriers have better coverage, but if traveling to the thinner populated western states, I'll be sticking with Verizon. No experience, so no comments on TMobile or other companies.
As for phones, we've had both Droids and iPhones, and while the iPhones cost more up front, I wouldn't go back to any of the Droids due to ease of use and availability of applications.
And a final comment... I was one of those folks that swore I'd never get that much use out of a smart phone. Said the same thing at one time about GPS navigation systems. While I can't say that I actually NEED either, the value I get from both of these technologies is such that I really wouldn't travel without them. Hershey's list on the first page of this thread lays out a number of the potential benefits, but there are many more beyond those.
