Wiktionary
n. (context US telecommunications informal historical English) Collectively, the family of company associated with http://en.wikipedia.org/wiki/American%20Telephone%20&%20Telegraph, providing telephone service in the United States for many years through 1983.
Usage examples of "ma bell".
It was a pleasure to hang up on that droning voice - it was too easy to imagine some great globular Directory Assistance monster buried somewhere in the earth, sweating rivets and holding thousands of telephones in thousands of jointed chromium tentacles - the Ma Bell version of Spidey's nemesis, Dr Octopus.
In return, Ma Bell would allow a hookup with equipment in the Tri-states.
Sort of like she had a direct brain-to-phone link to the fair world's Ma Bell and entertainment networks.
He agreed, and we set up the doubly secured relay, with me supplying a few bells and whistles that would make anyone trying to trace either one of us end up chasing their own tails through Ma Bell's systems.