Paradyne COMSPHERE 3920Plus Technical Reference Manual page 278

COMSPHERE 392xPlus Modems
Auxiliary Cables Not Supplied
To add an external telephone to your modem, use an external "Y" cable to connect the phone line
to both the modem and the telephone (Figure C-2).
Figure C-2. Wiring Diagram — "Y" Cable for External Telephone
C-4 October 1998 3920-A2-GH30-40