Intensified monitoring of inmates' phone calls from New Plymouth Prison has led to drugs charges against three people outside the jail.
Corrections Department central region intelligence manager Dave Alty says one of them faces 22 counts of supplying P, or methamphetamine, and possession for supply.
Random recording of calls began two years ago and all prisons now have the capacity. Recordings can be passed to others, including police, Inland Revenue and Work and Income, but calls to the Ombudsman, lawyers, MPs and some government agencies are exempt.
In the year to July more than 26,421 calls were monitored, 419 of which were found to be suspicious.
A step too far - penal reformer
The president of the Howard League for Penal Reform, Peter Williams QC, says that random monitoring is a step too far: it's detrimental to prisoners, he says, to know they may not be able to have a private conversation with family members.
With inmates often far from home, Mr Williams says, phone calls become the sole link with family and are thus essential to inmates' psychological welfare in the lead-up to their release.
He says there should be reasonable cause to suspect crime before bugging prisoners' calls.
Privacy concerns not allayed
The Privacy Commission says it is impossible to tell if the monitoring of prisoners' phone calls is intruding on their privacy.
The commission has long held that targeted monitoring is preferable, and the Corrections Department says that in practice that is what happens, but commissioner Marie Shroff says the department's reassurance is not enough to silence potential concerns.
If random monitoring occurs, she says, it could breach the privacy not only of prisoners but also of their families and children.