The electro-mechanical switching equipment required for their operation was rapidly becoming obsolete, supplanted by electronic and digital switching equipment.
The new telephone exchange equipment offered vertical service code calling features such as call forwarding and call waiting, but often was incompatible with multi-party lines.
One of the last manual telephone exchanges with party lines in Australia was closed down in 1986 in the township of Collarenebri, where most town residents had a telephone number of only three digits, and to make a call outside the exchange area it was necessary to call the exchange to place a call.
Secondly, if any party on a given line should so be inclined, there was the insidious opportunity to listen in on other parties' calls.
To signal specific subscribers on party lines selectively, telephone operating companies implemented various signaling systems.
The earliest selective system was the code ringing system, in which each telephone subscriber was assigned a specific ringing cadence, (not to be confused with modern ring tones).
Although various systems were implemented, one that limited the number of coded rings but established a uniform and readily understood format, was to first give the subscriber number as individual digits, which could be from one to four digits long per exchange, separated by the instructional word "ring" followed by the two digits of the ring code where the first digit indicated the number of long rings, followed by the second digit indicating the number of short rings.
Thus spoken, for example, as "nine, three; ring two, two" to mean subscriber No.