Voice Mail Preview will literally transform the way that you look at voice messages in Exchange. Exchange Unified Messaging (UM) makes it easy to manage your voice messages by delivering them in your Inbox. You can then use many types of Exchange mail client software to review your voice mail. Microsoft Outlook, Outlook Web Access (OWA), Outlook Mobile (and other clients connected via Exchange ActiveSync) and, of course Outlook Voice Access (the speech access interface in Exchange UM) are examples of the ways that you can now retrieve voice mail.
More info: Exchange Team Blog