There has been lot of confusion recently due to Microsoft banning many players for playing MW2 before the release date (most of these gamers were using illegal copies however).

Anyways, Robert Bowling from InfinityWard has said on his Twitter
"ANY store selling #MW2 early is in violation of street date. There are no "special permissions". That said, we won't punish players for it."

So if you have the privileged of getting the game early you can now play online with no fears of being banned

Enjoy!