The three way system or voice conferencing system allows call to be extended to third party when call between two persons is in progress. This is done by using external equipment or using the facilities available in the telephone exchange. The three way call is available in most of the telephone equipment used in homes.
The calls made by inmates can be extended any where using three way conference systems. Thus inmate can call the number they are not authorized to call. They can make threatening call using this or may conspire with other inmate using the three way call equipment. The terrorist can make use of conference system to hatch new conspiracies. To avoid this kind of abuse the use of three way calling is prohibited in inmate telephone system.
It has been estimated that around 10% inmates try to make 3-way calls and most of the 3-way calls are related to crime. In past the recording of these calls have helped in prosecuting the inmate for the crimes committed by them. But apart from this 3-way call have lead to harassment of general public when inmate make threatening calls to the crime witnesses and other persons involved in the episoide.
The three way call can be initiated by any home user by just depressing the telephone cradle switch briefly (half a second). This short break in signal tells the telephone exchange that 3-way call is desired by the subscriber. This causes the inmate on the line to be put on hold & dial tone is received by the subscriber to initiate another call. The subscriber then makes another call and when the call is through he/she has to just depress the hook switch again briefly to put make three party conference call.
It has been mandatory for all the inmate telephone systems to have 3-way call detection and disconnection feature.
However, it was found that most of the cases the 3-way call detection system was effective only in 30-40% cases as against claims of 80-90% made by the suppliers of these systems. Moreover the inmates have sharp mind and always find the ways to defeat the detection of 3-way calls by making loud noises, singing or tapping on telephone mouthpiece etc.