Carrier coverage maps are provided by each carrier to depict approximate coverage areas.  Obviously, actual coverage may vary due to terrain, weather, signal strength, customer equipment and many other factors. Clarity and reception may be diminished by obstructions such as buildings and foliage.  Carriers cannot guarantee coverage, however, it is our mission to help identify these persistent poor coverage areas, "poke holes" in their maps and inform consumers  when problem areas will improve. What you should know about wireless phone service FCC.gov

Consumer Reports Data Summary