I'm talking about the days of yesteryear, when there were not enough copper lines for every American to have (or want) a phone in their home. Typically a bunch of houses on a street shared a single line, known as a "Party Line." The operator or phone company switching office would use a sophisticated method of digital signalling (yes, digital signalling) to alert the parties on the line who an incoming call was for. The Jones's might be one ring, while the Smiths across the street might be two short rings.
I vaguely remember that our family had one of these lines when I was very young, living in the San Fernando Valley (California). I remember that people would blow a whistle on the line when a rude party would refuse to give up the line for an outbound call. I also remember picking up the phone to call my grandparents and hearing other people on the line in conversation.
Things have sure changed. I bet many kids in America cannot imagine sharing a phone with anyone -- even their parents.