I've been using Skype for a development project for a while now and despite some misgivings about security, I like it a lot. It works well as a basic text chat client, but it can also be used for voice chat and of course video. I find that the novelty of video chat wears off pretty quick, and nobody needs to see me looking weird at my desk, but voice chat can sometimes be handy. The basic version is free, but if you pay for a subscription you can initiate multi-way conversations, which can be very useful.

I leave Skype running all the time on my main computer, so as long as I'm at my desk (Skype status: online) you can reach me at jeff.rivett. Those of us who have been playing on the BF2 server are using Skype to alert one another when we're available to play. Feel free to join in!