IMHO, there should be a standard "courtesy-area" signal which would instruct suitably-configured phones to turn off audible ringers; once such a thing became common, anyone whose phone sounded off in an area where the signal was in use would be subject to public disdian.
The signal would not block receipt of text messages, nor prevent emergency (or other) outgoing calls (though someone who made outgoing calls discourteously would not be looked upon kindly). It would, however, help people who intend to be courteous to actually do so.
That sounds like a reasonable solution if and when the technology is perfected.