PRI DID's are assign target lines. These can indeed be set to appear and ring on a set just like analog lines as you have done, but they are phantom appearances.

If you transfer the call it is no longer on your target line and it becomes available for another call and therefore goes dark.

You can try putting the T1 lines on the phone (lines 1-12) and see if they remain lit.


Marv CCNA, CTUB
TeleMarv Services (Retired)
Providing telecommunication solutions in Ottawa Canada since 1990