Shoutbox

Most school's block these, but online versions of msn messenger could be used like the official one webmessenger.msn.com/. Or even a less known one that that school doesn’t know of, that isn't blocked.

Also even though the installation of new software may be blocked, there are still ways you can get past that, if they download the executable and are able to use an exploit to install it even though it's blocked.