With Exchange Server 2010’s new messaging waiting indicator feature, my customer, from a school district in Colorado, was trying to get this to work.
Here is a reference I found created by David Howe:
To enable MWI
1) Open Cisco Unified CM Administration
2) Click System > Security Profile > SIP Trunk Security Profile
3) At the Find and List SIP Trunk Security Profiles screen, click the FIND button
4) You’ll likely then see at least two SIP Trunk Security profiles (i.e. Non Secure, Secure). Select the profile used by your SIP trunk with Ex2010UM.
5) From the SIP Trunk Security Profile Configuration menu, verify that Accept Unsolicited Notification is enabled.
Note: If your SIP trunk to UM is configured to use Digest Authentication, also be sure to select the option Enable Application Level Authorization.
6) Commit changes by clicking Save (this will restart all trunks associated with the security profile)
For more on Exchange Server 2010 Unified Messaging visit here.