http://en.wikipedia.org/wiki/Cell_Jammer

http://electronics.howstuffworks.com/cell-phone-jammer.htm/printable

http://technology.timesonline.co.uk/tol/news/tech_and_web/gadgets_and_gaming/article2889295.ece

Be careful, there are some legal issues with their use... But to my understanding in your private home you may use them as much as you like

There are a couple on ebay from what I can see here too...