There was a thread on the subject a couple of months ago on the PPRuNe BB. (Professional Pilot's Rumor Network)
http://www.pprune.org/cgibin/Ultimate.cgi
It included reference to cell phones accidently left on in crew luggage in the cockpit, they appearently do have an effect on aircraft instrumentation, which can be noticed a moment before the offending phone rings for an incoming call! Digital phones have the potential to cause more problems then analog.
Went back and found the thread:
http://www.pprune.org/ubb/NonCGI/For...ML/009824.html
[This message has been edited by Old Gold (edited 11-10-2000).]