VATPAC Tutorial: CTAF, Unicom and VHF2 Monitoring
When flying through uncontrolled airspace, a pilot shall monitor UNICOM 122.8 and where other pilots would benefit, broadcast their intentions on that frequency. VATPAC also encourages the pilot to use the designated CTAF frequency at an uncontrolled airport however this does not replace the pilot's responsibilities under the VATSIM Code of Conduct.
Australia uses CTAF (Common Traffic Advisory Frequency) for radio comms at uncontrolled airfields. During an event, the Pilots is requested to tune the CTAF as stated in the flight event details. Pilots should also be aware that it is a VATSIM CoC (Code of Conduct) requirement that all pilots at uncontrolled airfields should monitor UNICOM on 122.800. It is highly recommended that pilots ensure that at least one of their "on board" COM radios (COM 2 being the most likely) is tuned to receive unicom transmissions in addition to transmitting and receiving on the published CTAF frequency.
Now for the interpretation, if it's likely that any pilots in range will benefit from a UNICOM call, that call should be made. If the pilot knows that ALL other traffic in the range is listening to their call on the CTAF, the additional UNICOM call will not benefit them. At the end of the day, if in doubt make the call on both.
The Guard frequency 121.5 is not to be used as per the code of conduct.