BitlBee is a chat-to-IRC gateway application. It lets you chat with friends on ICQ, MSN, GTalk, Jabber, etc. using an IRC client.
BitlBee is an external application that does not connect with Emacs at all, but it can be very useful if you wish to use one of the built-in IRC clients to speak with people who don't use IRC. Please refer to the official BitlBee documentation for information about how to set it up.