For $48 a company called “Deal Extreme” sells a “personal cell phone signal blocker device” - Perhaps the best or worst gift you can possibly give this year. Instructables member “Blastwavelabs” bought one and it appears the jammer ships set to frequencies outside North America but it can be modded to work by turning the trim pots a bit (small potentiometers to tune/trim the voltage)… I’m not sure that would actually work that great without a spectrum analyzer, either way a fun read and please feel free to debate in comments about why a device like this is needed