Jamming wouldn't be very effective. They would have to block the
> entire 800, 900, 1800 and 1900 MHz bands to get all cellulars, with
> enough power that they would splatter them within at least 1/2 mile
> around the facility (if not more) - and that would miss things like
> Nextel iDEN service, commercial radio, amateur radio, and other
> services. And if they have the capability to do spread spectrum that
> would make it even harder to stop.
That is the real problem. Radio signals don't stop at property lines. If you jam all the cell phones in a theater, you take out several surrounding office buildings too, at least intermittently. A rule of thumb I've used in ham radio is that if a signal goes 1 mile reliably, it will go 10 miles a lot of the time and 100 miles some of the time. And similarly for any distance.
Now what might work is a device to detect that cell phones are in use and complain about them. Cell phones transmit an identifying signal periodically even when you're not talking on them, so that the towers will know where they are.