Some places in various countries are installing mobile-phone jammers. Although ringing cell phones can certainly be a nuisance, the jammers are an over-reaching "solution" to the problem and may cause serious problems which could dwarf the minor ones they stifle.
I would suggest that a better approach would be to standardize a cell-phone "courtesy" signal which, unless overridden, would cause suitably-equipped cell phones to disable the audible ringer while keeping other features (vibrate, messaging, etc.) active.
Additionally, I would like cell phones to provide a button which would answer the call with a message that the holder of the phone would be taking the call shortly. This would allow someone who was e.g. in a movie theater when the baby-sitter called to discretely leave the auditorium before having to take the call [anyone who thought they might have to take a call would, of course, be asked to seat themselves along the aisles near the back of the theater].
These features could thus avoid much of the 'social annoyance' associated with cell-phones without reducing their usefulness for emergencies, family and otherwise.-- supercat, Oct 17 2004 I was just searching pre-post for exactly what you've got in para. 2. Thank you, and bun.-- lurch, Mar 23 2008 Yesterday on the freeway I found myself fantsizing about a mobile cellphone jammer, which would hopefully increase safety in the area around me.
Then I realized it would probably only increase the volume of dropped calls and people redialing in my vicinity.-- normzone, Mar 23 2008 random, halfbakery