TracFone uses AT&T, Sprint/T-Mobile, Verizon Wireless and U.S. Cellular, depending on the phone model. The models that do not use sim cards to connect to a network typically utilize Verizon or U.S. Cellular. Most Motorola models utilize AT&T, while most LG phones utilize Sprint or T-Mobile.
Unlocked contract phone services, prepaid services, like TracFone, do not have their own networks. Instead, they purchase airtime privileges from the major carriers who do. The way in which a carrier is determined for pre-paid phones is determined by the inner workings of the phone and how the phone connects to a network. Most cellular phones use sim cards. A sim card is a very small chip that contains all of a phone's information. When the phone makes contact with a network, the network authenticates the phone's information before it allows the phone to connect to the network. As phone technology continues to improve, however, more phone manufacturers are making their products without sim cards. This provides certain benefits to carriers. Sim cards can be removed and switched from one phone to the next regardless of model as long as both utilize the same type of sim card. This means that a phone with a sim card can bounce from carrier to carrier. Phones without sim cards and phones that have unique cards are "locked" and exclusive to their networks.