This would require that you use seperate exchange mailboxes for each user, one for voicemail and one for email.
When you configure a UM subscriber, you tell it what exchange mailbox to place the voicemails into. Unity UM servers don't have any local (when all systems are nominal) message store. The messages must be delivered to an offbox exchange/domino mbx. It's up to you to pick which one.
Hope this helps.
