The Economist wrote on this subject last December:
http://www.economist.com/blogs/babbage/2011/12/avionics
"Every airline flight you are on has at least a handful of mobiles, laptops and other electronic kit left in a standby mode or actively on, rather than shut off as aviation regulators and airlines demand. Every flight, in other words, tests the proposition that hardware carried on board by passengers disrupts the aircraft or confuses the crew with false readings from cockpit instruments. And yet airplane electronics, or avionics to use the technical term, do not routinely squawk or fail. ..."