Maintenance documentation and best practices guides exist for almost all of the devices involved in the Cisco Unity solution. They are a great place to start when it comes to learning how to monitor your voicemail system.
Links to UCBU's Maintenance Guides and Checklists can be found here:
http://www.cisco.com/en/US/products/sw/voicesw/ps2237/prod_maintenance_guides_list.html
