It was promised that there would be cheap modifications to most models of NAV and COM radios available - what has happened to that? Most FM immunity upgrades that I've heard of have involved brand new expensive kit rather than a mod.
The biggest risk of FM interference is to ILS due to the 105-108MHz band now being available for commercial radio stations.
This may not be the official word from the CAA, but I have been informed by an avionics engineer that in Private category aircraft the CAA is happy with just 1 x FM immune VOR/ILS and no FM immune radios as long the Nav kit is suitably placarded... useful for people with seperate NAV and COM boxes.
Obviously I'm not condoning that one should not follow the regulations to the letter
cheers!
foggy.