AT&T

AT&T (American Telephone and Telegraph) is one of the largest telecommunications providers in the United States. It is also noted for being the birthplace of the Unix operating system, and the C and programming languages.

History
AT&T was incorporated in 1885, but traces its lineage to and his invention of the telephone in 1876. As parent company of the former, AT&T's primary mission was to provide telephone service to virtually everyone in the United States. In its first 50 years, AT&T established subsidiaries and allied companies in more than a dozen other countries. It sold these interests in 1925 and focused on achieving its mission in the United States. It did, however, continue to provide international long distance service.

The Bell System was dissolved at the end of 1983 with AT&T's divestiture of the Bell telephone companies. AT&T split into three parts in 1996, one of which is, the former systems and equipment portion of AT&T (including ).

Wireless services
AT&T's 2G and 3G services are based on GSM and its derivative UMTS, respectively. was the iPhone's first exclusive carrier until February 10, 2011, when rival carrier Verizon released a CDMA-capable iPhone 4, ending Apple's exclusivity agreement with AT&T.

Devices exclusively carried by AT&T

 * iPhone
 * iPhone 3G
 * iPhone 3GS
 * iPhone 4 (GSM)
 * iPad
 * iPad 2

Retirement of 3G service
AT&T is scheduled to shut down its GSM-based 3G network in February 2022. This will affect all older iPhone models that do not support (iPhone 5C, 5S and earlier). This will also affect the 3G-enabled original iPad and iPad 2.