What your cellular providers claims is their coverage area and what their actual coverage area is can be two different things. OpenSignalMap offers a glimpse into the real world coverage of multiple cell providers.
Hit up the site, plug in the zip code you want to survey, and then check out the coverage either via tower density or a signal heat map. The map includes 2G, 3G, and 4G providers and coverage. Hit up the link below to take it for a spin.