Despite strict ban, mobile phone jamming devices are quite popular in the US http://www.slate.com/id/2092059/
and can be purchased online e.g. http://www.phonejammer.com/home.php
It is a bit pricey but I think the world would be a better place if more people used them to interrupt idiotic and highly annoying chatter in public places, such as restaurants or trains.
Wojtek