Want to have users be prompted to record their name and change their voicemail password at first login? Here is the link with instructions. http://www.trixbox.org/forums/trixbox-forums/help/voicemail-auto-attendant
However, the simplest way to go is to add the following in /etc/asterisk/vm_general.inc:
forcename=yes
forcegreetings=yes
In this scenario (and not in the link's instructions), the voicemail's password must be the same as the extension number. As well, if the user ever changes the voicemail password back to the extension number, the user will receive the intro message again, but will only prompt the user to change the extension's password again.