I did a lot of troubleshooting on a Partner Mail installation, and discovered some things that happen automatically when you assign an extension port to Hunt Group 7 (voice mail). Check these out:
The port will get Intercom First, but the Intercom Dial Tone will be "machine", ie, it will sound like an OUTSIDE dial-tone. BUT, if you look at #309, it will still be unchanged.
The port will NOT ring until the VMS Hunt Delay (#505) has been reached, EVEN THOUGH is you look in Centralized Telephone Programming you will see the lines have Immediate Ring.
All calls coming to the port will be accompanied by "Mode-Codes", ie, Touch Tone digit strings just after answering that indicate "why is this call arriving". This tells the Voice Mail what to do: Answer with the Auto Attendant, answer with a mailbox, log into Voice Mail, etc. If the call arrives without ANY mode-codes, Voice Mail will play "Transferring to Receptionist" and send the call to Ext. 10.
Some installers will remove all the line appearances for the VM ports, and that's OK, it'll still answer incoming calls, BUT the users cannot use Outcalling if the system allows it.
If you expand the number of lines on an exsisting installation, you don't normally use #104 but use #301 to add the lines indivudally to each extension. Don't forget to add them to VM ports also, so they also can be used for outcalling.
Some time when you have a new system that you can play with, program only one extension into Hunt Group 7, connect your Butt Set to it, and play with it to see some of the things that automatically happen. It's pretty interesting, and can help with troubleshooting other problems!