Infinity Ward has posted the following update on their official forums.
"Wanted to keep you informed with the information we're getting back from the server team. They have made some updates which they feel should resolve the connection problems. If you are still experiencing issues, please provide us with as much important network information as you can, for example:
What's your Router
As much info as you can provide, so we make sure everyone is taken care of.
As always, please let us know if you are still experiencing problems so we can keep the server team on it for you.
A patch isn't required, this issue is unrelated to the game's code. It's a Networking issue with the servers being slammed by the amount of people playing Call of Duty 4: Modern Warfare.
The only real issue is that the servers we're getting hit really hard, especially with the launch in Europe doubling that traffic, just something that requires optimizing on the server side and we've been working with the PSN COD4 Server team from the moment it started having issues assisting any way we can to help them get them up to speed faster.
Thanks for all the patience everyone, and this will not be a long term problem and as I said is merely server downtime issues."