If you worry about cell phones, please don't come to my club field. Three quarters of the fliers, including myself, have cell phones on their belts or in pockets. We have yet to see a problem.

I think a lot of the warnings are to protect the manufacturer and national organization from product liability law suits.

As for having a phone close to a radio, I don't run my battery lead near servo leads, if possible and I run the receiver antenna out of the fuselage and away from battery and servo leads. If's just good practice. I would imagine putting a cell antenna very close to any other type of antenna could cause some swamping or interference, but I don't thing you would get any after a couple of feet.