A conference call service 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.

Conference calls service 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 into a special 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. Via: Wikipedia.com