[alexmunroe]

I believe there was an issue with guards needing to be able to use their mobile phones in an emergency. The majority of the Prison service use TETRA radios now which can be linked in to the rest of the UK mainland emergency services so it shouldn't be an issue but there seemed to be a lot of reluctance so that there was a backup in the event everything else failed.

[cbr]

The people I know who work in prisons in the US aren't allowed to take their phones in. At least here the guards wouldn't have phones to use in an emergency.

[omh]

I think that TETRA are very similar to GSM phones, in both the technology and the frequencies. So it would probably be hard to avoid any jammers interfering with them.