On two occasions that I can think of I failed to turn off my phone (including FLL-ORD on Sun).. I thought it was off, then discovered upon landing that the phone was still on. Whoops! I'm still here to write this note.

Of course, the claim was never that ONE phone would cause the problem. What if EVERYONE on the plane had their laptop on and phone going during landing? I have no idea if it would matter.. but the issue isn't what one puts out, but that if you allow it you allow EVERYONE to do it.