A PBX, or Private Branch Exchange, is a private internal telephone network system typically used by companies. The basic function of a PBX telephone system is the management of incoming and outgoing calls of a company's telephone network. With a PBX, a number of internal extension telephones can be connected as well as some outside lines.The whole as well as specific departments in small as well as medium scale businesses can easily communicate among employees, transfer calls to other existing extensions, and receive phone calls from clients. An operator is sometimes required for manually routing calls, especially on older style PBX; however newer systems offer automation that improves control over the telephones in a company.