David Linstrom, in charge of technology in the Corrections Department, said blocking cellphones was one tool to stop "many of New Zealand's most dangerous and antisocial individuals" from organising more crime from behind bars.
While jamming technology was in all 19 New Zealand prisons, he conceded the systems are not designed to "provide full site coverage but are directed to the designated prisoner-accessible areas".
"While jamming technology restricts cellphone use, some prisoners spend large amounts of their time attempting to subvert our security systems and continue to obtain cellphones anticipating they might work," said Mr Linstrom.
On any given day, around 8600 prisoners are in custody and Mr Linstrom said there were thousands of movements - between prison, court or police facilities - as well as personal visits from lawyers, family and friends each year.
"While searches are undertaken every time a prisoner enters prison, and after every visits session, all these contacts represent an opportunity for contraband introduction."
Auckland lawyer Davina Murray is facing criminal charges of smuggling an iPhone, cigarettes and a light to a high profile killer in Mt Eden prison.
She has pleaded not guilty and says her 80 visits over 9 months to Liam Reid, sentenced to preventive detention in 2008 for the rape and murder of Emma Agnew, was to help prepare an appeal against his convictions.
The number of confiscated cellphones was not recorded by Corrections before December 2009.
But a high profile drugs case - conducted before jamming technology was introduced - revealed how inmates used cellphones to conduct business with one another.
Detectives in Operation Web bugged the phones of dozens of prisoners at Paremoremo, Spring Hill, Wanganui, Wellington and Christchurch.
The phones were also used to call China to organise the smuggling of pseudoephedrine to New Zealand, which was then manufactured into methamphetamine.
Among those convicted for running the P ring was Arthur Taylor - recently successful in appealing a smoking ban in prisons - and King Cobra leader Rocky Pulete.