The term “Private Automatic Branch Exchange (PABX)” is often used as a synonym for “telephone system”. Private automatic branch exchanges are switchboards which connect several devices, e.g. telephones or faxes and answering machines with each other and with the public telephone network. This allows a number of phones to be operated using a relatively low number of public telephone lines. Internal calls can be placed free of charge without using the public telephone network. Depending on the type of telephone system and the configuration, internal lines can be called directly from outside by using a direct dial in number, or indirectly through an operator.
Private automatic branch exchanges typically offer a number of features to make communicating significantly more convenient. Key components include toggle, conference calls and picking up calls. Toggle is used to switch back and forth between multiple calls. With call pick-up you can answer a call to an unstaffed phone from your own phone. With conference call several subscribers can be included in a call and everybody can talk with all parties to the call. Other typical features of private automatic branch exchanges are callback, call waiting, call transfer and call forwarding