The telephone circuit is a system of wires and switches that transmits sound and pictures over a telephone line. The circuit starts with the telephone lineman, who connects your house to the telephone line. The telephone line went into your house through the plumbing, so the telephone company can monitor your installation and repair it as needed.

This long, thin wire is twisted together at intervals to create the circuits in your telephone. Each wire carries both the audio and picture signals simultaneously. The telephone company sends signals over the wires to the switchboard, which directs the signals to the appropriate telephone.