Well, I guess that answers my little question of why my GFCI's would trip inexplicably in the kitchen awhile back, and it's stopped now - I turned in my Nextel over a year ago, and even when the charger was not plugged into the GFCI (plugged in on the line side of it) it would still occasionally trip, I had removed the phone from the troubleshooting equation.
I hadn't had a trip in a long time, and had forgotten about it. I never knew a radio could trip a GFCI.
Now if I only had $400-800 to purchase that Standard
I would be interested to know the EMC standard that UL943 references. I have access to the EN61000-4-3 standards. If one knew the volts/meter they test the GFCIs to then you could estimate how far away a given radio (at a given power level) would need to be kept from the GFCI wiring to prevent a false trip.
I have no direct experience with cell phones but they are typically a much lower power level that the type of radios that would cause GFCIs to trip. Not that they couldn't, just have not heard of it. Chargers often put a lot of noise onto the electrical lines and so conducted noise could also come into play and would not necessarily need to be downstream of the GFCI.