This could be a major concern for some of your drive time. Almost independent of which carrier you use, coverage will be good in urban areas and along Interstate Highways, and practically nonexistent elsewhere. The reason is simple. It just isn't cost-effective to stick cell towers up every few miles through hundreds and hundreds of mile of farm and range land on the off chance that somebody some day may want to make a call. While coverage along Interstates is usually fair to good so as to accommodate truckers and other travelers on these arterial routes, these highways were designed to get you from city A to city B in the shortest time possible. That is typically the antithesis of what people do on 'hit all the states' RoadTrips, wandering hither and yon in order to cut off a part of state X here and a corner of state Y there. The only way to do that is to use local roads. To be fair, from what I can make out of your map, you seem to eschew the shortest possible route to hit all 48 contiguous states in favor of following Interstates for the most part. If I am correct in that assessment, then you will have coverage for most of your trip. It will be spotty at times when you're relying on the towers along the highway as your sole connection points, but manageable.

AZBuck