You must set expectations. You will have strong 5G/LTE coverage in all cities (New York, Los Angeles, Chicago) and on interstate highways.
- National Parks: You will have a good signal in the "gateway" towns (Flagstaff, Jackson Hole) and at the main visitor centers and lodges (e.g., Grand Canyon Village).
- Deep Wilderness: Once you are on remote hiking trails or in the deep valleys of Yellowstone or Yosemite, you must expect long "dead zones" with no signal from any provider.