Surely faraday cages and cell-phone jamming would be easier and less restrictive for regular people. (The BBC article says they're changing legislation to allow them to block signals in prison) From the BBC article:-
> More than 7,000 phones and Sim cards were confiscated in prisons in England and Wales last year.
(https://en.wikipedia.org/wiki/United_Kingdom_prison_populati...)
> Using the figures below from 2009 and 2011, the UK prison population stands at around 97,000. As of October 4, 2011 the population of women in prison in the UK is 4,635.
I don't know how many phones they're not finding. Or how long prisoners have had phones before being caught.
[1] Although England and Wales sends too many people to prison and there was a problem with women not paying tv licence fines, and then going to jail for not paying the fine.