Though four wires are typically used in U.S. phone cabling, only two are necessary for telecommunication. In the event that a second line is needed, the other two are used. They are also sometimes used to provide power for telephone dial lamps (6 volts AC, as in the Princess phone), or other features.

What wires connect phone jack?

5:496:50Wiring a Home Phone jack - YouTubeYouTubeStart of suggested clipEnd of suggested clipThe blue goes on the red post and if you have two lines then the on the orange white pair the orangeMoreThe blue goes on the red post and if you have two lines then the on the orange white pair the orange white goes on the black and the solid orange goes on the yellow.