I see a few posts recommending faraday cages in theatres.
This has 2 obvious problems:
1) Faraday cages require an actual cage. Doors and other openings might prove problematic.
2) 911 calls. The FCC would not be cool with blocking all access to 911.
I have a better idea. Mandate all phones sold in the USA MUST prioritize joining a specific theatre carrier over all others. We'll call this carrier STFU and whenever a phone sees this carrier it must join to it instead of any other operator(AT&T, Sprint, etc) it might otherwise prefer. Our STFU carrier will then blackhole all traffic not destined to 911. Then put a low power antenna(cell tower) in each theatre covering all available frequencies. All SMS, internet and voice traffic not destined to 911 is then black-holed. Only outgoing calls to 911 work in the theatre. Everything else simply doesn't work. The theatre can then route all 911 calls via it's existing land-line. Which emergency services prefer anyway because they get an immediate address when the call comes in.