I have a pair of SC 3 line 3 hold phones from the 60's or 70's. They have normal 10 volt lamps under the hold keys, and neons under the line keys. The line keys will flicker during ringing and the hold key will light up on the active line when you lift the handset. All the wiring is brought out in the mounting cord so you can connect a few together and the lights are common between the sets. I just have them powered from some 9VAC wall wart I had laying in the junk drawer. The neons won't work from the ringing voltage of most ATA's and they certainly don't work off my partner, but now that I'm running everything from a channel bank, they flash brightly when the line rings.