Have a UC520 and the customer has 6 mobile users that do not have a physical phone. They do have an extension only for a mailbox and this extension can be dialed internally or via a DID and all that works fine and you can leave the users a voicemail. But, the users cannot set up their voicemail. When they initially dial into their voicemail, Unity gives them "Sorry, this mailbox can only be set up by the extension for this mailbox, please setup from the extension for this mailbox" or something similar. How can it be set up so they can setup their mailbox just by dialing into unity?