To expand on that, AT&T had a regulated monopoly. You were not allowed to attach non AT&T devices to their network, and they had the only network (and no one else could set one up by law). You did not own a phone, but leased it on a monthly basis.
When the telephone answering machine was invented (not by AT&T) you could not legally attach it.
The plus of this arrangement was that AT&T made devices that would last for decades, all areas of the country got service (regardless of wealth or population density or politics), and costs were not surprising. The minus of this arrangement was that innovation was stifled and some costs were artificially high. It became a competitive disadvantage that was holding our country back from innovation. There is a correlated timeframe between the breakup of AT&T and the massive expansion of the computer industry.
