That said, Verizon had good coverage for most of my trip. There were dropouts in the hills of Virginia, Kentucky, and Missouri, but most of the towns had coverage even there. Coverage was pretty solid from central Kansas westward.
The "problem" is that a company has to put up towers every 10 miles or so, and it's just not cost-effective to cover every hollow and valley where the population density is low. I was surprised that the Grand Tetons and Yellowstone had cell coverage (not so in Great Smoky Mountains, which makes it hard for the boss to call me, which makes it a good vacation spot!).
Note that wifi is almost everywhere today in the U.S. Libraries (although they may be closed and you might not get access), most motels, and a surprising number of greasy spoons all have access points.