Hi Paul -
The best way I know to track this is to use Message Tracking on the Exchange server, using Exchange System Manager MMC. By selecting recipient and mail server(s) and selecting a date range, you can see the voice messagess being delivered to the user's inbox. Also, since this is an offbox message store, could someone else be administratively changing the recipient on a user's mailbox (this can be done on the user's user account in Active Directory Users and Computers). Ginger