PSTN Operators
The task of building the networks and selling services to customers fell to the network operators. The first company to be incorporated to provide PSTN services was the Bell Telephone Company in the United States.
In some countries however, the job of providing telephone networks fell to government as the investment required was very large and the provision of telephone service was increasingly becoming an essential public utility. For example, the General Post Office in the United Kingdom brought together a number of private companies to form a single nationalised company.
In recent decades however, these state monopolies were broken up or sold off through privatization.
Read more about this topic: Public Switched Telephone Network