Busted!!!! After considerable digging I got to the bottom to the "Popcorn Popping by Cell Phone" urban legend-- by consulting the web site "Snopes" -- it is an Urban Myth!
It was a stealth marketing ploy from a manufacturer of Bluetooth headsets to make people "scared" to put their phones to their heads thus prompting the purchase of hands-free headsets.
Clever? You bet your ass... Sales shot up over 100% for the company!
Great for them... but bad for we conspiracy theorists. :) I guess it's back to Loch Ness. *sigh*
See Below for the truth