AT&T Mobility LLC (branded and referred to as AT&T, formerly Cingular Wireless LLC) is a wholly owned subsidiary of AT&T that provides wireless services to 103 million subscribers in the United States, including Puerto Rico and the U.S. Virgin Islands. AT&T Mobility is the second largest wireless telecommunications provider in the United States and Puerto Rico below Verizon Wireless, which has 108.3 million customers as of the third quarter of 2011. AT&T Mobility is headquartered in the Lenox Park area of DeKalb Co. Georgia, just outside Atlanta.

Originally Cingular Wireless LLC from 2000 to 2007, a joint venture between SBC Communications and BellSouth, the company acquired the old AT&T Wireless in 2004; SBC later acquired the original AT&T and re-branded as "AT&T". Cingular became wholly owned by AT&T in December 2006 as a result of AT&T's acquisition of BellSouth.

In January 2007, Cingular confirmed it would re-brand itself under the AT&T name. Although the legal corporate name change occurred immediately, for both regulatory and brand-awareness reasons both brands were used in the company's signage and advertising during a transition period. The transition concluded in late June, just prior to the rollout of the Apple iPhone.

AT&T Inc. (sometimes stylized as at&t; NYSE: T, for "telephone") is an American multinational telecommunications corporation headquartered in Whitacre Tower, Dallas, Texas, United States. It is the second^{[citation needed]} largest provider of mobile telephony and largest fixed telephony provider in the United States, and is also a provider of broadband subscription television services. As of 2010^[update], AT&T is the 7th largest company in the United States by total revenue, as well as the 4th largest non-oil company in the US (behind Walmart, General Electric, and Bank of America). It is the 3rd largest company in Texas by total revenue (behind ExxonMobil and ConocoPhillips) and the largest non-oil company in Texas. It is also the largest company headquartered in Dallas. In 2011, Forbes listed AT&T as the 14th largest company in the world by market value and the 9th largest non-oil company in the world by market value. It is the 20th largest mobile telecom operator in the world with over 100.7 million mobile customers.