Thanks to some digging by Steve Hughes, there is a new Windows Live "toy" for IE Mobile users to enjoy. Windows Live Mobile Web Client allows you to use Windows Live Messenger for IM without the installation of a client. While this functionality has been around for the desktop for some time, it is exciting to see it come to the mobile world!
According to the Live Ideas Beta page, Windows Live Mobile Web Client offers a lot of features.
To access the service, simply point IE mobile to the following address:
http://mobile.live.com/wlm
That's it! You'll be IM'ing with your browser in no time!