KEY POINTS:
Telecommunication companies will use "jamming" technology to stop cellphones working in prisons under the agreement with the Government.
The technology will involve special jamming units being installed at prisons to block the frequencies into them.
Corrections was reluctant to discuss the specific technology they will use, but commonly jammers emit radio waves along the same frequencies used by cellphones to disrupt the signals and make the phones useless.
The jammers range from small, hand-held ones to large units of many kilometres radius.
Jammers are illegal for private use in many countries, including Australia, Belgium, Canada, and in the UK.
In New Zealand, blocking the signals in any area requires permission from all mobile providers in the area and any other provider of radio services operating on nearby frequencies.
In 2005, a push to allow it in movie theatres was opposed by the two telecommunication companies because of the potential effect on other customers in the same general area.
Jammers have been used to block communications, for example, during military or police operations, but some countries are now allowing wider use.
In France, they have been allowed for movie theatres since 2004 and Mexico allows them in banks, churches and movie theatres.
In Italy in 2005, cellphone signal jammers were installed in the Sistine Chapel after the death of Pope John Paul II to prevent information leaks from the conclave deciding on his successor.
Detection technology - used to find and locate mobile phones - will be used in areas too close to other users and where blocking is impractical, for example residential areas such as Mt Eden with a prison.
