Here are some field notes from a Lync 2010 environment using the telephony and integration to Exchange Unified Messaging for the Voice mail feature.
There was a problem changing the UM Dial Plan settings from Unsecured to SIP secured or Secured.
The following error may appear on the completion page of the wizard, when you change from unsecured to secured or SIP secured from within your Dial Plan is:
The following warning(s) occurred while saving changes:
The VoIPSecurity type of dial plan ‘UMDialPlan1’ doesn’t match the UMStartupMode of the following Unified Messaging servers: ‘EXCH-UM’. Make sure that if the UMStartupMode of the Unified Messaging server is set to TCP, the VoIPSecurity type for the dial plan is set to Unsecured. If the UMStartupMode of the Unified Messaging server is TLS, the VoIPSecurity type for the dial plan should be set to either SIPSecured or Secured.
You will have to make sure that the UM Settings has the Startup mode set to TLS or Dual.
To resolve this issue, open the Exchange Management Console – go to Unified Messaging under the Server Configuration. Right-click the unified messaging server you are using with your Dial plan and select Properties. In the UM Settings tab change Startup mode to either TLS or Dual.
After changing the setting, restart the Microsoft Exchange Unified Messaging service.
You can now change the VOPIP Security settings of your Dial Plan.
In Exchange Management Console navigate back to the UM Dial Plans tab under Organization Configuration > Unified Messaging. Open your Dial Plan and you can now change the VOPIP Security setting from unsecured to Secured.