On a different note, me and my friend and his wife went to see Roger Waters perform The Wall a couple years back. The tickets said "No photography", but the band was very careful to say "When you take photos, please make sure the flash on your cameras is off. There are effects during our production that camera flashes will disrupt." I'm paraphrasing, but they were projecting video on the bricks that were assembled onstage as part of the performance. Sure enough, not minutes into the first set, flash flash flash flash flash.
My friends were taking photos. I made sure not to look over at them.
It would seem letting people have a signal doesn't have to be a problem.
I think your definition of "disruption" may not be entirely reasonable. It's one thing if someone is sitting there having a chat during the movie, but if a person quietly getting up and excusing themselves (in response to an unheard vibration in their pocket) is unacceptable, then we're going have to ban anyone who sits down to a three-and-a-half-hour film with a Jumbo Big Gulp from the concession counter.