Instant messaging applications get blocked in lots of places. Some workplaces prevent you from installing software on your computer without IT approval so you can load the IM client. Then there are public computers, like those at libraries, where there are no IM clients available either. If you want to use IM in this situations, the easiest way to use meebo. They provide a free web-based IM client that runs inside a browser. So if you can open a browser window, you can chat with your friends. The service works with AOL, Yahoo, MSN, and Google Talk and it is free to use.