I am trying to get two PS3's with two copies of MW3 to play coop games. Oddly enough the two ps3's can be used to play group multiplayer online.
Here is how I am trying to get it to work.
1. Both consoles start up MW3.
2. Both consoles go to main screen where you can select ops, campaign or multiplayer.
3. One console goes to campaign and clicks the green triangle to access friends list.
4. Selects player on second console. The next screen does not have the "invite to party" menu selection enabled.
The same result happens if we try ops mode. However, if we attempt this with multiplayer mode it works. We can party together to play multiplayer. FWIW, neither consoler/player has finished campaign mode or ops. Both have started campaign mode though.