My oldest son was obsessed with MS Flight Sim as a kid. I think I bought him two or three versions that ran on Win95/98. He ended up getting hooked up with a group of people who had developed an open source Air Traffic Control simulator that plugged in to Flight Sim. He REALLY became obsessed with that.
Long story short, he's now works for the FAA at Miami Center as an air traffic controller.
Ha! That reminds me FS X had ATC built in with audio. There was this one little kid who would always try and boss everybody around. People would disobey him and taxi on active runways and stuff, just to piss him off.
But the host controlled the session and could boot you if he wanted. But then the guy would come back again.
I think we had more fun pissing that kid off than we did flying.
Other guys were more serious , they would set up a session with a flight plan Like JFK to ORD then ALB and LAX. You had to use certain planes and fly in formation. land IFR with like a 100 foot ceiling.
Glad it worked out for your son.