I have just discovered that Call Of Duty Modern Warfare 2 has cross game invite. I was playing resistance 2 when sand-man sent me a invite from CODMW2. Out of curiousity I tried joining from the messaging service whilst i was playing R2, and when i clicked join, the console asked me if I wanted to quit R2. I clicked yes and then it asked me to insert CODMW2 disk in and click ok, and when i did click ok it sent me into the matchmaking. There was no menus , it was heading straight for the lobby, with the message on screen telling me it was trying to join, but there was a problem at my end where the game crashes at this point. When sand-man tried it whilst he was in uncharted 2 and when he accepted my invite it worked for him. He went from uncharted 2 to CODMW2 with no problem the first time but other times there was problems like the game completely freezing and when you quit the game it reboots the whole system. It seems like there is a glitch in this cross game invite system or it could be a clitch with CODMW2 that needs fixing.
Also you accept to join a game invite from MW2 whilst your not playing any game from the XMB but that one also has a glitch where it gets to the lobby screen then crashes.

I really hope Sony or Infinity Ward fix this issue.

not just MW2, you could do on the lost planet 2 co op demo, and some others i cant remember