The problem is not primarily with the technology, but rather the fact that some people refuse to be discrete in their use of it (though there are a few technological tweaks that could be helpful). Actually, I would think that with some technological tweaks one could construct/program a cell phone such that a theater patron could communicate during a show without anyone being the wiser. Combine a headphone with a means of silently responding by touch only. No light to disturb other patrons, and no noise except the sound in the earpiece (which, being inside the earpiece, could be essentially inaudible to everyone else).
Why can't these people just get up and LEAVE THE ROOM, as a courtesy to the other PAYING GUESTS?