Each time you fly from somewhere to somewhere else, the crew go through the same procedure before take-off: Turn off all radio receivers and transmitters during the whole flight, and during take-off and landing, please turn off all electronic equipment.
The call for turning off transmitters, I can understand, though why you should turn off receivers, I am not sure. The call to turn off stuff like CD players and such is just silly; yes, they contain a small electromotor which will emit a bit of noise, but if the navigational systems of the plane are that suspecible to jamming and malfunction, I am really, really scared of flying.
The problem of having a rule like the one above is that you make those who know the factors involved question your judgement and make them ignore other rules which might actually matter.
