I have always had this issue Dave, but it doesn't come up frequently as most of the airports I fly to/from have at least a tower frequency. If the airport has no assigned frequencies, I cannot add it via the 'add a frequency' facility in PF3, as that crashes PF3 every time I do it, as I mentioned. I can probably do it by adding the frequency manually to one of the csv files an running the PF3 update..
But what I was asking was probably valid for FS2004 too - if you leave an airport without having contacted ATC, how do you get back in touch once you are en route? I try all sorts of likely frequencies, but even when I contact ground on arrival, tuning to the correct frequency, PF3 gives a little sound to show ,message received', but does no more. Seems if I can't contact ATC at the departure airport, PF3 is 'dead' for the rest of the flight. What would you do in FS9? May be that in X-Plane PF3 won't work if you haven't been able to make any contact with the departure airport, but just wanted to check the proper way in FS9 before I 'abandon all hope' for this in XP11.
Thanks.