IFR certified a/c - required on C of A?

[Contacttower]

I think I've found the answer; obviously in class G you can do what you want (including electing to fly IFR without FM immune radios/nav) except if you want to do an ILS approach inside or outside controlled airspace it must be FM immune. Inside controlled airspace VOR reciever must be FM immune for IFR flight as well.