Originally Posted by bigsaabowski

The plane I fly (a Delta Connection CRJ) was built before the BlackBerry was even conceived. It is impossible to test the aircraft's electronics with every possible portable electronic device, so the rule is not arbitrary.

This quote comes straight from the Pilot's Operating Handbook for my aircraft in reference to the cargo fire extinguishing system: "The use of cellular phones or mobile transceivers within close proximity to the smoke detectors can lead to false smoke indications." There is also evidence that cell phones interfere with the radar altimeters, the antennas for which are located beneath the last few rows of the cabin.

While an iPod player or a Bose headset are extremely unlikely to cause any interference, a smart phone running at max output (which it probably will be inside an aircraft, due to the low signal strength) of 2 or 3 watts can very well create problems.