Which carrier has the most extensive cell phone service coverage?

Verizon Wireless is the largest cell phone network in the United States with over 87.7 Million Customers within the United States. The second largest network is AT&T with over 77 million customers in the United States. Also, Verizon Wireless's network covers the most area in the United States when compared to all the other cell phone networks, however, AT&T's network is better for traveling outside of the continental United States, as there is better coverage in many different locations.