For Merlin 410 Basic:
There are Ring Switches located on the control unit. If the switches are in the Up position, the associated telephone will ring immediately when calls come in. Each switch that is in the Down position will cause the associated telephone not to ring.

For Merlin 410 with Feature Package 1 or 2:
This is individual programming and can be done from the telephone you need to change the option on.

1. Put any calls on hold and hang up the handset.
2. Slide the T/P switch to 'P' for program; the telephone will flash and ring every 5 seconds.
3. Check the red light next to each line button:
        Steady red = Immediate Ring.
        Flashing red = Delayed Ring.
        No red = No Ring.
4. Press the line button to be programmed until you get the type of ringing you want.
5. Slide the T/P switch back to the center or dot position.