Once you move into Day 2 support mode, continue to monitor your subscriber community. Their satisfaction is key to the long term success of the project.
Complete any lingering issues associated with the cutover.
Meet with users on a regular basis. Conduct periodic satisfaction surveys. Stay in contact with the powers users and the special users. Check with the key business units you listed earlier and verify the Cisco Unity solution is performing as expected.
Document any problems that are identified. Resolve the problems as quickly as possible and report your results. Do not allow negativity to build.