I always used to hear the old CRJ false cargo fire warning stories from the 90's and the correlation to cell phone usage when I was at my last company.
I've had strange caution lights come on and off before with no explanation, could be a coincidence, or maybe not.
We've all heard the buzzing in the headset though.... That link to cell phones is irrefutable.
Every electronic device, whether or not it is designed to transmit or receive signals, has an electromagnetic signature of some kind. I always get a kick out of those who don't want to turn off their Kindles or iPods at the gate because they think it couldn't possibly emit any type of signal. Better to be safe than sorry.