...target lines.
DIDs have their identity coded in the DID trunk circuits which carry (one at a time, not multiplexed) any one of the DID numbers you reserved from your provider. These identifying digits (usually people use the last four digits of the DID phone number)are mapped by customer programming to a chosen target line.
This is done by matching the incoming digit string to one of the internal Norstar target lines (check the manual for the number scheme). The target line, now with its DID number paired to it, is then assigned to one or more phones just as POTS lines are assigned.
Usually a person has a DID assigned to their phone for the purpose of providing them with a direct inward dialing number (DID). A group of salesmen, for example, may each have their own direct incoming number for their clients.
So, really it is a problem just of reassigning the target lines.
There may be some uncertainty regarding the DID & target line number schemes, but that is the heart of dealing with these numbers so as to yield a powerful, compact system.
Yours,
Mike