Re "Are all FIA frequencies ATC frequencies? Leaving that question aside ..."
For 'Flight Information Areas', the answer would be YES!
FIA = (Designated) Flight Information Area = talking to Airservices to gain information = ATC these days....n'est ce pas??
(There MAY be 1 or 2 'Flightwatch' VHF freqs left lurking somewhere in this 'wide brown land'....but if so, they would be very few and far between.....
No??
You can tell me that I'm wrong again....I don't mind - its been a while.....
Cheerrrssss