Sorry - if you track my posts you will find I have asked many questions about using un-towered airports.
When getting near to the destination airport, Approach cancels your flight plan and instructs you to re-tune. How do you know the channel for Unicom or Multicom? I'm probably missing something here but I have been through the manual and cannot see any pointers. It doesn't seem to always be FSX's defined channel, if indeed one is defined at all.
John