Users are unaware when they have reached the max number of voicemails. They only find out that it is full when someone tells them they couldn’t leave a message. An alert email to the mailbox owner would be ideal. Along with this, the ability to batch delete voicemails would be helpful too. Most of our users listen to their messages through the computer and therefore forget to delete from the phone. If there were an option to delete all, that would be helpful.
If memory serves I think there may be a prompt to delete all read voice mails, but +1 on the alert if full. It should not just be an email, as not all users may have email, but to include a voice prompt from the system to users when checking VM that will inform that the VM box is full and until they delete messages, the box is unable to accept new.
+1 batch delete (all or unread)
+1 notification (speech and/or email)