Cell phone jam

I have been irritated so many times, in the cinema, by mobile owners. Either it is the loud ring-tones or plain lack of etiquette. It hasn't happened so much here as in India. Partly because the message 'Switch off your cell phone' is repeated so many times before the movie. In fact Orange ads featuring such messages are laugh out loud funny, and looks like they work.
In India on the other hand, we still continue to be inconsiderate. Blame it on whatever -the ignorance of social mores, need to talk incessantly, or just showing off the latest gadgets.
So, the theater owners should just go ahead and buy a cell-phone jammer. I don't think there is any law NOT to jam cell-phones in a cinema-hall. So it won't be illegal at all. Anyway, where there is law, there is loophole. So, why not use a loophole for good.