Thanks for your reply. Actually what I was looking for was what is run to connect the users' voicemail box number (301, 302 etc) to asterisk so that you can dial in to get voicemails. I believe this script actually creates the voice messaging when someone dials in (for John dial 1, for Sarah dial 2).
After some sleuthing around on the web it appears that you need to write this information to /etc/asterisk/voicemail.conf. Since mine was completely blank, I went looking around on 8.10 and found that the permissions need to be set asterisk:asterisk. Mine was set as www-data www-data.
so the command I ran was:
chown asterisk:asterisk /etc/asterisk/voicemail.conf
After checking that this worked I went to wizard\basic info\users and deleted and added back a user.
I then opened voicemail.conf and found it fully populated with all users. When I went to telecom, my voicemail and general voicemail I could now see my voicemail instead of receiving the login button. Hope this helps someone missing their voicemail.