Naughty Dog Dev, "ReklissAbandon" slipped up with this little tidbit of info earlier.....
"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."
The comment has now been removed, but hopefully this will become a reality as it has been something the PSN community has been asking for. read