My cricket bat says the person sitting next to me will seriously regret using their mobile phone if I'm asleep.
Thing is the dicks that can't shut up for five minutes already use their phones on planes regardless of whether it's allowed. And usually at the most dangerous points of any flight "Hello.. yeah we're taking off!" How vital that must be for the loved ones back home to know, almost as irrelevant as "Yeah.. we're landing on the runway right now.. it'll be another 30 minutes before I get off, and up to an hour before I get my bags, then go through customs and immigration. So yep, you're absolutely right, there was no point at all in me risking making this call right now - it could easily have waiting until I got to the terminal, or even when I was collecting my bags!"
And while admittedly the risk of the plane blowing up is pretty low just because someone used their phone - having the instrumentation going screwy while making a landing in zero visibility is generally the sort of thing I'd prefer to avoid.
"What? I've buggered up the ILS? I might be a bit late then, bit of a bumpy ride at the moment - was that one of our wheels I just saw fly past the window?!"
Again, small chance. However one thing I can absolutely guarantee has a massive chance of occuring - almost 100%. If you wake me up on a flight, shouting your personal life down a phone for the benefit of everyone sitting within 1/2 a mile of your obnoxious self - you'll personally find out whether cell phones double as anal sex toys.