Maybe from a ride on a private airplane? The Cessna I used to fly had solid 1960 technology in it, not much chance of a cell phone disturbing sensitive electronics, in fact I believe it's recommended to take you cell phone with you in case your radio fails, so you can still get in touch with ATC.

Besides, the other day on an Eagle flight, when I wanted to switch off my cell phone, I noticed that it was in my rollaboard, in the luggage compartment. I decided to keep quiet about it, because if I had told someone, I bet they would have had to reopen the door, find my bag, switch off the cellphone etc., and I'm pretty sure that a cell phone is not going to crash a plane... I then turned it off before boarding my connecting flight, though...