I would want a password to retrieve Voice Mail Via the Auto-Attendant.. if not, anybody who figured out the VM menu number could just press it and get VOicemail for anybody at the company with just the extension number...I think you could have a touch tone to have it go to the collect voice mail for a certain user by matching the caller id.. but not sure if that would get around the password..
I just checked for myself, and you can allow it to go to the messages with no password for users, just set them up under user start points for collect and have it point to get mail with the users mail box.. then make a goto to goto the start point for collect on that user.. no password needed.. there might also be an easier way to do same thing.. didn't poke into it much.-