OK, don't skip slots, so move the Partner Messaging to the 2nd slot (do this with the power OFF)
From left to right slot 1: 206E R4.1
slot 2: partner ACS partner messaging
slot 3: Partner ACS processor 3x8
slot 4: empty
slot 5: empty
Look at the PCMCIA card that is in the Partner Messaging, to see if it is labeled 2 Ports, 4 Ports, or 6 Ports.
Now from Ext. 10 or 11, press Feature and dial 00. Press the Left Intercom button twice
Dial #505-7-24-1
Dial #399-24-25
If you have a 2 port card, press Feature and dial 00
If you have a 4 port card, dial 26, 27, then Feature 00
If you have a 6 port card, dial 26, 27, 28, 29, then Feature 00
This would be your starting point. You'll probably have more questions coming, but now Intercom 777 should get you into voice mail. Make sure that you can get there 3, 5, or 7 times in a row, on the 1st ring.