A previously banned phone-jamming technology was activated at the maximum security Lithgow Correctional Centre on Tuesday.
While it is illegal to operate, supply, or possess jamming devices in Australia, NSW prison authorities received special approval from the Australian Communications and Media Authority (ACMA) for the Lithgow trial.
Dozens of antennas inside Lithgow Correctional Centre will jam the channels that normally transmit mobile phone signals during a nine-month trial.
Corrective Services commissioner Peter Severin said the technology would help stop inmates from organising crime from behind bars.
"We believe this jamming technology is the ultimate answer, because even if an inmate does obtain a mobile phone, it will be worthless because it won't work," he said.
Shutting down the use of smuggled phones by prisoners has long been a challenge for jailers.
In July, it was revealed that convicted murderer and Lithgow inmate Bassam Hamzy used a contraband mobile phone to run a drug ring between Sydney and Melbourne.
Corrupt prison officers have also been caught smuggling phones and other contraband to inmates.
In January, the Independent Commission Against Corruption (ICAC) found that Long Bay officer Karaha Pene Te-Hira accepted thousands of dollars in exchange for smuggling mobile phones and chargers, SIM cards, steroids, and mail.
Telstra, Optus, and Vodafone are cooperating with the trial and will monitor the results.