Along with the release of a native Java and Windows Mobile version of Live Messenger for Mobiles Beta, Microsoft also has released a web browser based Windows Live Messenger for mobile devices.

Simply navigate to mobile.live.com/wlm/imsi.aspx from your mobile web browser and sign in to Live.com account. Once you sign in, the first option displayed is whether you want to show yourself Offline or Online (or even Away, Busy,etc) just like the desktop messenger client. After selecting the mode, you should be able to see your contact list and chat with them right away.

Under Settings, one can choose to hide offline contacts, display buddies by their email address or display name and the option to show icons along with text or just plain text.
Other customizations include adding and deleting contacts and changing appearance.