Cross-game chat is one of the few remaining features that the PSN is really lacking before they can legtimately compare themselves to the XBox 360's Live service.  According to rumors, the feature was supposed to make the cut for firmware 3.0, but it was pulled last minute until it was compatible with the console's full back catalog of games.

However, according to a Naughty Dog developer,cross-game chat is on the way.  Speaking on the official PlayStation message board in regards to the ability to spectate the enemy after you die in Uncharted 2's elimination mode, a Naughty Dog dev going by the handle ReklissAbandon, let it slip the feature would hit in the next firmware update.  The original post has since been deleted, but we managed to copy it down before so.

"I think they wanted people to have fun and ejoy the show since all dead players can talk to each other no matter what team you are on. But I will suggest it anyway. Not to mention that the next PS3 firmware update is going to allow cross game chat. So if players use that instead of in game communication then they would also be able to communicate enemies positions."

Hopefully the Naughty Dog dev didn't get in too much trouble for letting the cat out of the bag on that one...