You have to run the domain prep and forest prep steps or this will not work. Just follow the installation guide provided on previous post as it will state that those steps need to be taken as part of the Exchange setup.
Yes, the message store CD should be in the same bundle as the Unity software. (not the OS discs) Also the datastore (SQL)
If you are install Voicemail only onbox, then you need to install Exchange. This would involve all the steps required by Microsoft to install Exchange into a new Active Directory. The Unity install guide covers this.
You can not have (2) separate Exchange servers in the same forest. Well, you can have multiply Exchange servers in the same domain/forest, but they will be in the same Exchange Organization. This means they share the same address book, rules, etc. So if you placed this other VM Unity server running Exchange into the customers "production" AD domain, you will have to figure out AD accounts, and Exchange mailboxes. Basically, John Doe will his production AD account and Product Email account. Then for Unity Voicemail Only, he will John Doe -Vmail account and John Doe -Vmail Exchange account.
In regards to two months and with this question, are talking about a brand new Unity Voicemail only install, or an existing Unity voicemail only?
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.