On the Iwatsu ADIX, it was common to simply send forwarding extensions and 9 plus the originating extensions to voicemail systems.
If you wish to retain this simplicity behind a Repartee for Windows, you need to edit the AVANALOG.AVD file.
Add the lines:
Data36= 9I DIRECT
Data37= F NOANSWER
Data38= 9 OPENING
Data39= 77xxx OPENING
to the [ADIX] field.
Data 36 prompts for a password when retrieving messages, Data 37 plays greetings associated with forwarding extensions, Data 38 plays the default opening greeting for extensions dialing the voicemail system, and Data 39 sends all trunk calls to the opening greeting as well when 77 is used in the ADIX as a trunk call packet.
Be careful to retain the spaces between fields in the AVANALOG.AVD file. The above example should be used as reference for the data, not the format. I suggest you copy and paste Data 35 and edit it appropriately.