In-Game Messaging

I imagine people have asked for this before. Just about any game has either added this over the years or has had people ask for it but not get it for whatever reason. I realize that there are additional problems when you add a way for people to communicate with each other in the game including how to make sure nobody says anything inappropriate. Still, as far as I know the only way to talk to someone you meet in the game is to find them on Facebook and add them as a friend (Facebook charges you to send a message to someone you're not friends with). It would be nice to have a way to communicate with the people you meet in the game and add as friends within the game. For that matter, it would be nice to have a way to communicate with everybody in the game, even if they're not your friends in the game. It could be as simple as editing the e-mail notification section to act as an all-around in-game e-mail system. Would it be possible to add some sort of method of interpersonal communication in-game?