Trillian does accept messages from the other services, and Trillian is free, not some big company's offering. So they have less of a legal problem.

That said, I tried it in a previous build, and really didn't like it. However, I've heard some good things about the latest version, which is apparently completely different, and figure it's worth trying again.

If you have friends who prefer different IMs, then it's worth a try, because IF you like it, you can uninstall the three-four others that you are currently using.

Right now my fave is ICQ, but I also have friends on yahoo, aim, and msn.