Many areas of the West have poor cell coverage, regardless of carrier. Here in Montana, coverage is good near many towns, and along the freeway corridors, but generally on State and Federal highways between towns you can forget it. Oh, you might catch a tower from the top of a hill somewhere, but you will lose it in a half mile or less.
Verizon seems to be the best bet here, or one of the pre-paid plans that use the Verizon network, such as Trac-Fone.
wi-fi will not be found at the best camping spots (state parks and Forest Service campgrounds). Most of them don't have cell service, either.
Many commercial campgrounds have wi-fi, but it often isn't very good. "Adequate", but not "excellent". Some of the out-of-town RV parks don't have cell service.
