Levi Wallach published a good comparison of wireless data plans from the major U.S. mobile phone carriers. If you want to know what the cost and features of the wireless data offerings from T-Mobile, Cingular / AT&T Wireless, Verizon Wireless, and Sprint PCS, this article is a good place to start.

One of the things that harder to gauge by reading this article is the extent of coverage that carriers are currently offering. Wallach says, "Cingular... already has a national EDGE network built out with great coverage...." and refers you to this very complex, PDF-based coverage map from Cingular.

I can give a more concise example of the coverage of Cingular's network in comparison to that of T-Mobile, the other GSM-based national carrier in the USA; Cingular has voice service and GPRS service in some built-up areas of Vermont. T-Mobile, on the other hand, doesn't offer voice service in Vermont at all. When my wife, Kathleen, and I go to Middlebury to spend some time where she went to college, we make sure we bring her mobile phone which runs on AT&T Wireless.

Is Cingular's faster, more available mobile data service worth the premium that they charge above T-Mobile? You have to decide that. The same thing goes for the price difference between Verizon and Sprint PCS, since they also run technologically-comparable wireless data networks.