Back in the day, with Hogwarts Online and The Establishment, we used AIM. Things could get confusing with multiple people in a room, but it had the advantages of being able to set logging, and with Trillian, you could have multiple characters running at once.

In fact, I've just logged in to the long-distance D&D game I've been part of for five years now. Each player has two character windows, plus an OOC chat open. It works surprisingly well.