Further to this functional deficiency, was a twofold practical deficiency.For though one was only to answer one's own ringing code, every party on the same subscriber line could hear all the ringing codes.Farmers in rural Australia used party lines, where a single line spanned miles from the nearest town to one property and on to the next.although subscribers in all but the most rural areas may have had the option to upgrade to private-line service at an additional monthly charge.Many jurisdictions require a person engaged in a call on a party line to end the call immediately if another party needs the line for an emergency.Such laws also provide penalties for abuse by falsifying emergency situations.
Secondly, if any party on a given line should so be inclined, there was the insidious opportunity to listen in on other parties' calls.
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.
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).
More selective ringing methods were introduced using various technologies.