BIK, early cellular phones did have a tendency to cause electro magnetic interference with AM radio signals, but nowadays with the digital networks and closer monitoring of radio telephone frequencies it isn't much of a problem.
I suppose if the Pilot in question were navigating with his ADF and the pax were to be using an early analog phone there may be troubles. I think the regulations haven't changed because nobody has seen fit to do the research necessary to determine how much interference handheld electronic devices can cause with basic VHF/UHF equipment. Not to mention the fly by wire, and auto pilot/throttle systems on so many aircraft in use these days ( I see you mentioned that at the end of your post ).
