AT&T held a monopoly in the US and Canada, throughout most of the 20th century. AT&T was the owner of the Bell System, a network of telecommunications companies which included Western Union Telegraph. For many years the slogan of the company was "One Policy, One System, Universal Service."
However antitrust regulators were not happy with AT&T and in 1974, the United States Justice Department opened a case against the company, arguing they were violating the antitrust law. This case was settled in 1982, and the company was order to break up. Hence AT&T was divided into seven Regional Bell Operating Companies.