You will have to have the same aircraft installed as the other guy, to see it in Multiplayer.

I dont think you can use FS atc in multiplayer, but there is always vatsim or something like that 

Hi Aviator
In multiplayer, you will need to sort your CSL file to see other aircraft as what they are. I have done this with help but don't ask me how to sort it, you should go to www.vatsim.net and try and find out the info or post on the forums there to try and sort it.
As Tom says, atc is not available in mutiplayer buit if you try flying on servers like vatsim or IVAO you will find the live ATC a fantastic experience, vatsim is the only place I fly now, tho setting up the software is not for the fainthearted.