I have CIX 1200 systems with DKT3210-SD phones. Some of the phones have multiple incoming lines on them. I am being told that when on a call and another line starts to ringing, the user hears the ringing in the handset.

I thought this was a feature that can be shut off. Don’t remember how to do it. Can anyone help?

I have had this in the past and from memory a simple unplug the phone and plug it back in fixed it.

Try msg volume down?

Try Telephone Programming Mode?
Call Waiting and Camp-on Ring Tone Over Handset/Headset Option
1. Press 3+6+9+ (simultaneously).
2. Press 0.
3. Press Feature Button 4 (FB4) to toggle On/Off.
FB4, LED On: Call Waiting tone
FB4, LED Off: No Call Waiting tone
4. Press Hold to set the option.
5. Go off-hook, then on-hook to exit the program mode.