You may have noticed in your environment that, while enabling Unified Messaging in Exchange the option 'Automatically generated SIP resource identifier' is selected by default. But oly enabling Unified Messaging in the Active Roles’ WI the option is not selected and is greyed out.
This is a product defect (TF00694143).
This will be fixed on a future release of the product. A public hotfix addressing this issue is expected to be announced after the release of the upcoming maitenance release: 7.0.4.