Cell phone jamming is the up and coming tech, of course. Used to be a neat-o spy tool for making an area secure, now available for restaurants, movie theatres, etc. It's basically just an area-of-effect in which your cell phone gets no signal. So if you're a classy restaurant who'd like to ban cell phones, but don't want to strip-search people to keep the phones out, a cell phone jammer makes a lot of sense.
Next project: hand-held directional cellphone jammers, so you can select an individual obnoxious person and take their signal away.
Dan