The phones will be rendered useless when the latest generation mobile-phone jamming is switched on at Goulburn's Supermax 2, the high-security unit for extremist and terrorism-related offenders.

The system includes numerous antennas, which jam the frequencies that would normally transmit mobile-phone signals.

Testing of the system's first stage roll-out begins today (August 26) and will later include the rest of the Goulburn Correctional Centre and the original Supermax.

Commissioner Peter Severin said Corrective Services NSW (CSNSW) was a leader in implementing technologies to combat contraband in prisons.

"Contraband mobile phones are an issue for prison authorities around the world, because the phones are as small as a key ring and can be easily concealed," Mr Severin said.

"This technology will make a significant improvement to the security at Goulburn because even if an inmate manages to smuggle a phone in, it will be completely useless for communication because it can't connect to the network."

Minister for Counter Terrorism and Corrections Anthony Roberts said the technology will complement existing anti-contraband measures at the prison.

"Mobile phones and other contraband pose a threat to the security and safety of our correctional centres, which is why we take a zero tolerance approach," Mr Roberts said.

"The specialist Security Operations Group and correctional centre staff conduct frequent searches of visitors, vehicles and inmates. We use x-ray and other scanning technology, intelligence gathering and targeted and random searches of cells and common areas."

The Australian Communications and Media Authority made an exemption to the Radiocommunications Act 1992 for the phone-jamming trial at Goulburn. If the initial testing is successful, a two-year trial will commence.

The system at Goulburn has been installed so the jamming signal doesn't penetrate beyond the complex's boundaries and doesn't affect mobile devices in the community.

The technology was first trialled at Lithgow Correctional Centre in 2013 where it remains in operation.

The 46-bed Supermax 2 opened in May to act as a 'step-down unit' from the original Supermax. It houses offenders who have demonstrated a commitment to disengage from radical behaviour.

It is currently housing Supermax inmates while the original centre is being refurbished.

For enquiries call 1800 526 637 (1800 Jammer).