Prisoners have made 1500 calls since the middle of last year to report suspicious behaviour or turn in other criminals.
About a third of the calls to Crimestoppers came from inmates at the Otago Corrections facility. Those held in Whanganui prison made none.
Police have been unable to specify how many of them have been acted on, or have led to arrests, because the phone line is anonymous.
Even so, Corrections says inmates are now offering crime tips far more than they used to.