From your description, it sounds like you have an ACS processor and an expansion module along with a 2-slot carrier, giving you no room for expansion modules, and your voice mail system is a PCMCIA card in the processor unit.
Let's try and make this easy. Go here
to see the programming overlay for your phone.
At Ext. 10, press Feature and dial 00
Press "System Program" (Left Intercom button) twice
Dial #505-7-10
Press 2
The bottom line of the display says "2-Not Assigned"
Now press the button for "Next Item", and the extension number will increment
Again dial 2 and confirm that the bottom line of the display says "2-Not Assigned"
Keep pressing Next Item and dialing 2, until you have hit every extension number from 10 through 57.
When you get to 78 and 70, press 1 to make it Assigned.
When finished, press Feature and dial 00 to exit
Now you should be able to press Intercom, dial 777, and hear "Welcome to Avaya Partner Voice Messaging