The telephone router is used to select which phones get the ring signal from a telephone line. It works with the distinctive ring feature available from the telephone company. When the incoming call is received, the first ring is used to identify the number that has been called. The telephone equipment for the called number is then connected to the phone line and then allowed to ring.
Some of the common uses would be for routing calls to a home office, fax machine or just to route calls to different members of a family without disturbing others. The privacy feature can be used so that others do not inadvertently interrupt faxes, internet connections, or conversations.