Basically, it says that in-flight there is potential they can interfere with navigation equipment. That this lessens the safety margins and that it can be really dangerous during take-off and landing phases of a flight.
but... it also says that they estimate at least 1 phone is left on (perhaps intentionally) during the average flight (not in 'Airplane mode' but with antennas activated and transmitting). And up to 4 in an average flight.
So they build up this strong correlation between cell phone usage and possible navigational interference (ironically, the one actual example of navigation interference came not from a cell phone but a portable DVD player) but then they leap to the conclusion that these all count as "incidents" qualify as near misses for an accidents. Estimating that 6.5% of all accidents were due to personal electronics.
This is a stretch, these guys are brilliant and I'm only mildly-intelligent (on a good day), but an RF interference does not equal a safety incident. One can simply not say that all RF incursions and interference with aircraft avionic equipment creates an inherent safety risk.
Pilots fly planes, not computers, and there is a good reason for this. There is clearly a great potential for disaster if the norm becomes computers taking off and landing aircraft but we aren't there yet.
Clearly an argument could be made that any interference with the proper operation of aircraft avionic equipment, especially navigation, reduces the safety margin but context is important.
If I'm driving down the road and a bird craps on my windshield it has, technically, reduced my safety margin -- but my reaction determines to what extent -- if I panic or freak-out then it's a big loss but if I remain calm and take corrective action things are fine.
This is not to say I disagree with the results of the report. Merely, the conclusion that personal electronic devices have caused flight accidents.
And frankly, if they are as dangerous as these fine gentleman purport, then I would expect some terrorist jerkoff, somewhere would be taking advantage of it to down aircraft.
Yes, phones should be off during takeoff and landing (especially-especially-especially in rough weather conditions or darkness when instrumentation becomes vital) but when you're sitting on the ground? Taxing? No one claims that's a safety risk.
Clearly communicating actual dangers and implementing regulations that target them specifically and not in an overly broad fashion would be far better than the "We are the MAN! Turn your phones off when we shut the door or we're throwing you off the flight!" attitude.