9696d660_Exchange_Voice_Mail_User_Guide__Description
[Feature] MWI (Message Waiting Indicator) [How to Enable or Disable] Send email to itcom.csr.evm@umich.edu to have this feature enabled (or disabled) Note: this features is not available on Centrex phones [Description] 
Lets you know when a new (unopened) message is in your mailbox. (Note: if you mark the message as unread, MWI will appear again.)
ITS Exchange Voice Mail User Guide
Description