Speaker and microphone

• Perhaps the two most obvious parts of any telephone are those parts you directly interact with: the speaker and microphone. In modern telephones these two components are contained in the handset. These components are attached by wires to the duplex coil.
  
  

Duplex Coil

• Because the microphone and speaker are connected to the same circuit, without any additional technology you would hear yourself in the speaker. Because this can be distracting, telephones have a duplex coil to sort out your voice from the other person's voice.
  
  

Hook Switch

• The hook switch connects and disconnects your telephone to the local telephone network. When you lift the phone off the cradle, the switch connects creating a closed circuit to the telephone network. This is where the phrase "off the hook" comes from. When you put the phone back onto the cradle, it creates an open circuit and disconnects the phone from the network.
  
  

Keypad

• Before keypads were included on telephones, you would have to call the operator to connect you to another person. The keypad allows you to pass sound frequencies through the telephone network to connect you to other people. The keypad can also be used to interact with automated telephone systems.
  
  

Ringer

• Between the wall jack and the other components of the phone is a ringer that signals when a phone call is incoming. The ringer has to be placed before the hook switch so that it can ring without your phone being actively connected to the phone network.