Pre-Flight mental check

On the flight from Gatwick to Edinborough Saturday afternoon, the flight attendant reminded us to switch off our mobile (cell) phones since they “interfere with the systems of this aircraft.” It occurred to me that this is highly worrying because either this is

a) a blatant lie, or
b) very, very bad news for my brain cells

If it is, in fact, a blatant lie, then I’m a little worried about what else the airlines might lie about. I mean, if they’re willing to scare me with visions of crashing planes just to keep me from having annoying phone conversations during a flight, then what will they do to keep me from putting my seat back?

Also, I’m fairly sure that plenty of people have gone a whole flight’s worth of time without remembering to turn off their phones. I assume that planes calibrate their equipment before they take off---so if you realize halfway through a flight that you never switched your phone off, is it better to leave it on (and hopefully continue to screw up the instruments in a consistent manner) or to turn it off (and risk throwing off the pre-flight calibrations)?

We may never know. Of course, it also might not even matter.