AT&T, Verizon and Sprint are the three largest telecommunications companies in the United States. They offer wireless voice and data service as well as wired services, such as landline phone and Internet access. T-Mobile is another large company, offering wireless voice and data service.
All of the four largest telecom companies offer wireless service throughout most of the United States. They provide 4G LTE networks in most major population centers, in addition to maintaining older networks still in use. Many smaller telecom companies use the networks of these larger companies to provide service in limited local areas as well as contracting with them to provide roaming service.