It seems Activision has stopped caring about Modern Warfares online servers. This has been going on for about a week now.
I've reported it to activision. Everyone should do the same. You can do so by going to Support > Contact Support > Select PS3 Platform > COD Ghosts > Multiplayer > Problem not listed and then go to LIVE CHAT Support.
Make sure you say it's about COD4 2007 non-remaster of course on PS3. The more people that do this the more it'll be reported to their technical teams and the higher chance of it being repaired!