Southwestern Bell is an American telephone company . It was consolidated under the management of a single management unit of the Bell System with Southwestern Telegraph and Telephone Company of Texas-Arkansas , Pioneer Telephone and Telegraph Company of Oklahoma , and The Bell Telephone Company of Missouriâ '' also called The Missouri Bell Telephone Companyâ '' on March 1 , 1912 . These companies comprised the `` Southwestern System '' of the Bell System .