A conference call is a telephone call in which the calling party wishes to have more than one called party listen in to the audio portion of the call. The conference calls may be designed to allow the called party to participate during the call, or the call may be set up so that the called party merely listens into the call and cannot speak. It is sometimes called ATC (Audio Tele-Conference).
Conference calls can be designed so that the calling party calls the other participants and adds them to the call; however, participants are usually able to call into the conference call themselves by dialing a telephone number that connects to a "conference bridge" (a specialized type of equipment that links telephone lines).
Companies commonly use a specialized service provider who maintains the conference bridge, or who provides the phone numbers and PIN codes that participants dial to access the meeting or conference call.
The more limited Three-way calling is available (usually at an extra charge) on home or office phone lines. For a three-way call, the first called party is dialed. Then the Hook flash button (or recall button) is pressed and the other called party's phone number is dialed. While it is ringing, flash / recall is pressed again to connect the three people together. This option allows callers to add a second outgoing call to an already connected call.