The easiest way is just to have Coverage forthat D-I-D Extension. But that has the limit of only 8 extensions can cover it.
The 2nd easiest way is to use what we call a "LOOP AROUND".
This requires a "SPARE" T&R Extension port, and a "SPARE" Line Port.
The Extension Port would be re-numbered to the D-I-D number.
Then you would connect a cord from that T&R Extension Port to the Line port, mantioned above.
Then, you just assign that LINE to all the phones you want to have an appearence of it.
Any number of phones can have an appearance of that "LINE".