I work at an airfield in Class 'G' airspace, with an ATZ (no class 'D' protection) and published Instrument approach procedures which involve a hold situated over the airfield which can be active up to FL65.
If you flew through my overhead without talking you would
NOT be flavour of the month
The GA airfield I fly from (A/G service only) has an NDB on the airfield, which is used for IMC training (in VMC only of course). The initial level of the procedure when flown is 2400' QNH - 200 ft above the ATZ.
Still think it's a good idea to just 'listen'?
CM