as far as I know, there is no way to toggle back and forth between auto login (press the message button from your ext and it logs you in automatically, bypasses "enter your password then press#) Unity Admin is the only person that change this behavior on and off.
The only way I have used this type of setup is for Admins and Execs with UM. With Outlook\Exchange... you can setup shared access to their inbox. If the exec has voicemail, the admin would open her outlook, then his or her shared mailbox to view the voicemails.
It would have to setup a "shared password" for the group. Or if you want to get fancy, Change the number from a greeting to a Call Handler:
"Hello, you have reached the voicemail box for Office Services, please leave a message.. if you would like to leave a mesage for John Doe, press 1"
Then 1 could go to John Does mailbox. May or may not work... but its a shot.
