This may be a dumb question, but I don't use facebook (and don't intend to sign up)... But I have various XMPP accounts and I have friends who use facebook.

Does facebook allow chats with people on other XMPP-servers (like I'm on my ovi.com account, and you're on your facebook account, and we chat via XMPP) or is it just another interface to their closed "facebook only"-infrastructure?