Re: Ready for the down votes, but...
Jamming wifi is already covered - the FCC has bared its fangs a few times, but Ofcom is the kind of regulator who avoid doing anything.
Theatres and others can be locked down fairly easily. I know of one multiplex that was built with RF in mind from the outset (the owner was a movie enthusiast and pissed off about yammerers) and phones simply don't work once you go into the threatres. No jammers needed.
As far as IMSI or not IMSI is concerned: It's actually better to build genuine mobile cells at or close to the prisons and then have them lockout call access to anything within N metres of the antennas in the directions matching the location of the prison (It's perfectly feasible to lockout where distance is greater than N and less than M too, or direct them to an authorised tapping system)
The problem witch cracking down on mobiles in jails is that it's worth bearing in mind that the vast majority of smuggled phones in the UK are used to keep in contact with family, due to over-restrictive access to and overly high pricing for the in-prison phones, not for other ongoing criminal shit.
Isolated lags end up with higher recidivism rates upon release and lack of family contact is also linked to higher in-prison violence levels so this genuinely needs addressing as a matter of high priority - at which point anything left inside the walls should be more nefarious and able to be stomped on hard. The whole "retribution/revenge" vs "reconciliation/repair" thing needs to be sorted out because you don't really want a revolving door where going to prison turns people into hardened crooks who will only ever know prison or a crminal life outside. The IMSI stuff is only tackling one part of a hugely complicated mess.