One approach that some people have proposed to eliminate intrusive cell phone ringing is to jam or shield an area from the cell phone signal. Its actually surprisingly easy, but possibly illegal, to block the signal. A group in Japan has experimented with adding metal oxides to paint, a wall painted in this way appears to block cell phone reception.
I think this is the wrong approach, and not just for the standard "what about the doctor who much always be reachable" argument.
A better approach would be to standardise on a signal / text message / whatever that could be broadcast to a cell phone to request that the phone turn itself into vibrate mode. Movie theatres, resturants, etc. could simply broadcast this signal and compliant phones would become well behaved. Considering the venom we have for people who interrupt us with inappropriate cell phone ringing non-compliant phones might soon find themselves at a competitive disadvantage.
Alternatively, location aware phone like the IPhone could take a pro-active approach an notice their own location. Imagine being able to configure your IPhone so that whenever you were "near" a location on your Be-Polite-List it automatically went into silent mode.