There was an interesting article in The Wall Street Journal, maybe last year, saying that the ban on the use of cell phones onboard the aircraft is not an FAA regulation but an FCC regulation, that Boeing conducted tests by flying an aircraft to check if any interferences can be observed and found out they could not, etc. It also said cell phone uses are banned onboard not because they interfere with navigation systems but rather airplanes fly so fast that phone companies do not have software to check cell phone communications moving so fast from one anntenna to another -- All if I remember correctly. (You know, you can call onboard an aircraft using built-in phones.)

Are these claims still valid? Does anyone know?