I havent played it on my brothers xbox yet, so i dont know how the invite system works there, but on other games on ps3 you invite people through the game. With MW2 you send them messages to their PS3 inbox, which they then have to accept. Takes a lot longer than the old way because you have to open the XMB, go to your inbox, hit accept, instead of just getting a popup message in the game.
Fuck yea its free...you do realize that were playing the same game, on the same internet and youre paying for yours and im not right? Yeah, I'm the sucker. Shit I could even smooch wireless off my neighbors network if I wanted and play completely free.