A conference call is a call where the caller wishes to have more than one person listening in. Conference calls can be designed to allow a recipient of the call to participate during the call or a call can be set so that the recipient only listen to the call and can not speak, this is often referred to as the ATC or 'Audio Tele-Conference'.
Conference calls can be designed so that the caller calls the other participants and adds them to the conversation - however, participants are generally able to make a conference call by calling the special telephone number that connects to the "conference bridge" ( a specialized type of device that connects a telephone line).
Companies typically use a specialized service, which keeps a conference bridge, or by providing phone numbers and PIN codes that participants dial to access a meeting or conference.
Three way calling is available (usually at extra cost) for many customers at home or on the office phone line. For three-way calling, the first person is the one which makes the call. Then the hook flash button (known as the recall button in Britain and elsewhere) is pressed and the phone number of the other person is made. whilst the phone is calling, the hook flash is pushed again to connect the three together. This option allows callers to add a second call to a call already connected.