The airline I work for says that all mobile phones must be switched off, including phones fitted with a flight mode. The reason we as cabin crew have been given is that the CAA have not been able to test the flight mode of all phones and therefore cannot advise as to whether they are safe to be used.
Also, the use of electronic items on take-off / landing is not to do with interference. It is more based on the premis that using a video camera / walkman etc may distract a passenger from any safety related announcements.
HTH