The phone system we all know and have used since the turn of the 20th century is often referred to as the "plain old telephone service" or POTS. Phone lines are also referred to as POTS lines. POTS is an alalog voice phone service. The telephone microphone converts the vibrations from the sound of your volice to electrical impulses. The electrical impulses carry the vibrations across one or more copper wires to the central office, across a switchboard or automated switching device and finaly to the other phone at end of the electrical circuit. The speaker at the other end converted the electrical impulses back into sound.
This phone service is fast disappearing and being replaced with digial phone service. The telephone handsets in most households in the United States and abroad still utilize this type of service.