Set your cabinet up with the modules in the following order:

Slot 1: 206 module marked 18 through 23
Slot 2: 206 module marked 24 through 29
Slot 3: ACS Control unit
Slot 4: Partner Messaging module
Slot 5: 400 module

Plug in a phone, press Intercom, and dial 777 to reach the voicemail.