The Bell System comes to mind, which had a monopoly on telephone service for nearly a century & tightly controlled which devices could run on their network (so

The Bell System comes to mind, which had a monopoly on telephone service for nearly a century & tightly controlled which devices could run on their network (so they were kind of more analogous to something like "Apple+{Verizon+ATT+TMobile}"). Toward the end of that telephones were definitely the primary medium of communication.