AT&T Inc. is an American multinational telecommunications corporation, headquartered at Whitacre Tower in downtown Dallas, Texas. AT&T is the second largest provider of mobile telephone and the largest provider of fixed telephone in the United States, and also provides broadband subscription television services. AT&T is the third-largest company in Texas (the largest non-oil company, behind only ExxonMobil and ConocoPhillips, and also the largest Dallas company). , AT&T is the 23rd-largest company in the world as measured by a composite of revenues, profits, assets and market value, and the 16th-largest non-oil company. , it is also the 18th-largest mobile telecom operator in the world, with over 128.6 million mobile customers.