Straight Talk Wireless is on the Verizon network. It and other carriers that use larger companies' networks, such as Virgin Mobile and Boost Mobile, are termed mobile virtual network operators. As such, they have business arrangements with the larger companies and are not true competitors.
To provide service, these network operators purchase airtime from major companies, such as AT&T, Sprint, T-Mobile and Verizon, at wholesale prices. They then resell these minutes to the end user under their own brand. Without the cost of infrastructure to cover, these typically prepaid plans can be quite affordable, allowing consumers to enjoy a quality network at a lower cost.