In an effort to curb the widespread use of illegally smuggled cellphones in prisons, officials at Prey Sar prison a few months ago installed a cellphone signal jamming system, forcing inmates there to resort to prison-provided landlines, officials there said yesterday.

Sun Lean, chief of Prey Sar, yesterday confirmed the installation of the new system – which comprises a central tower and multiple transmitters – while declining to comment further. However, multiple guards, a prisoner and an NGO worker – all of whom declined to be named due to fear of reprisals – said from inside the prison yesterday that the new system had effectively ended the common practice of using smuggled cellphones.

A 28-year-old officer at the prison estimated yesterday that there was at least one smuggled phone per shared cell, a practice that has persisted despite the installation about a year ago of about 100 landline phones available for prisoners’ use.

Given the landlines' significantly higher price – about 38 cents per minute versus a few cents on a smuggled mobile phone – the phones went largely untouched until the installation of the jammers. “The system to block the phone signals operates around the clock,” he said.

A staffer from an NGO working to provide prisoners with health care said yesterday that prisoners had gone to great lengths to hide smuggled phones, with one inmate hollowing out a hole in a table to conceal his mobile.

However, the availability of the phones, he continued, at times proved problematic. “Prisoners are not allowed to call out whenever they wish. One prisoner called to threaten a victim from his cell. [Now] only 023 lines are available,” the health care worker said, referring to the numeric prefix for Phnom Penh landline numbers. “Other lines are blocked.”

One prisoner in his 20s who was working outside of his cell said the new system – in which prisoners must buy phone-credit cards, which are inserted into the landline phones during use – put an unfair burden on prisoners wishing to contact their families, given what he characterised as the prepaid cards’ exorbitant price.

“We need to buy PIN cards valued at $3, $5 or $10, [but] the $3 card could be [used up] within 10 minutes,” he said, noting that there were no other options. “We will be punished, and our mobile phone will be confiscated if the prison officers see it.”

At more than 30 cents a minute, the phones are more expensive than usual calls, even compared to phone stalls on the street. A vendor near the prison who provides phones to the public on a per-minute basis said yesterday that she charged only 500 riel (just over 10 cents) per minute.

Am Sam Ath, a technical adviser for rights group Licadho, acknowledged that phone use needed to be restricted inside prisons for security purposes, but nonetheless called on administrators to reconsider the rates for using the landlines.

“It makes it even more difficult for the poor, who cannot afford such a price.”

Cellphone jammers emit radio waves that “prevent the targeted device from establishing or maintaining a connection”, according to the US Federal Communications Commission.

However, guards inside the prison say they’re concerned for different reasons.

“I am working outside the cells, and I am OK, but the coworkers inside complain that they are having headaches due to the radiation system, which they really absorb,” one guard said.

The 28-year-old officer shared his concerns: “We are worried that it affects our health, like our hearts, muscles and nerves,” he said. “Our boss does not care about our health.”