Program the extension for "Intercom First", i.e. in Centralized Telephone Programming, dial * *, then the LEFT intercom button, then the lines in the order you want them accessed , then * * again.
If the extension is programmed for immediate ring, just turn it on when it rings on incoming calls.
To put a call on hold, "park" it by flashing, (which brings up intercom dial tone), and dialing you own extension number. To pick it back up, dial 6 and then extension number that parked the call.
To transfer to another extension, flash and dial the other extension. Hanging up the cordless completes the transfer.
For outbound, dial 9 and get the next available line, or dial 8 and the two-digit line number (801, 802, 803...824, etc.)
To pick up a call on hold, and you know the line number it is on, dial 6-8-and then the two-digit line number.
Note that users at a system phone can dial Intercom 6 and the parking extension too, as well as park calls by Transfer and their own extension number.