Overview: The latest version of Windows Live Messenger as of Sept 08.
Windows Live for Windows Mobile includes:
Integrated contact list (Windows Live and phone contacts) and option to not sync contacts
Windows Live Messenger
Windows Live Mail
Access to Windows Live Spaces (and capability to upload photos on some devices)
Windows Live Search (web search, location based search, etc.)

Uninstall previous version, then install this version. Install/Uninstall may lock up your device, but be patient and wait for it to complete (it is a very slow process ). A soft reset may be required after install and Uninstall.