Before World War II, the same telephone line was shared between two or more customers. Usually it was two to four homes sharing the same telephone line. In rural areas there could be as many as twenty parties on the same line.
There were various ring systems used to identify the customers on a line. Individualized rings for each home would be used, such as patterns of long and short rings. All the other homes on the “party line” heard everyone else’s rings thus alerting those interested, the opportunity of putting their nose in everyone’s business.