What is "ameritech"

AT&T Teleholdings, Inc., formerly known as Ameritech Corporation (and before that American Information Technologies Corporation), was a U.S. telecommunications company that arose out of the 1984 AT&T divestiture. Ameritech was one of the seven Regional Bell Operating Companies that was created following the breakup of the Bell System. Ameritech was acquired by SBC Communications in 1999 which subsequently acquired AT&T Corporation in 2006, becoming the present-day AT&T Inc.