I just found Vat-Sim. It supports FS 2004, and I'm not sure, yet I think FSX too. Has a huge multiplayer community. This is truly, As Real As it Gets.
ATCs (Over 100) use only real ATC terminologies to communicate with pilots, and the pilots are expected to respond correctly. There is no chatting allowed, after all, you don't hear pilots talking to each other (Hey, did you see that bugger? He almost rammed me... Heh heh heh)
To me, this is extremely realistic. I highly recommend anyone looking for a good FS 2004 or FSX community to check this out!
http://www.vatsim.net