A station dss button or dss panel button if programmed with a station number should stay lit while in use or while ringing. You can create a co line appearance on a station or dss panel button and it will light when ringing and stay lit while in use as well.

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"Old phone guys never die, they just get locked in some closet with an old phone system and forgotten about"

Retired, taking photographs and hoping to fly one of my many kites.