I agree that this isn't a good design. For it to work the Meridian Mail would need to automatically send all messages to the users mailbox **and** AMIS network them to Unity. If it can do that, Unity can deliver the message to the mailbox. MWI is not going to turn off after the user has read the voicemail through outlook.
Are you getting this error “Installer User Interface Mode Not Supported. The installer cannot run in this UI mode. To specify the interface mode, use the -i command-line option, followed by the UI mode identifier. The value UI mode identifiers...
The below trick might come handy when you have to add a new node to a cluster but you don't have or is unsure of the security password for the publisher. This procedure has been around for ages.
1) Login into the CLI of the Publisher.