A PBX  Telephone system connects your office user telephone extensions to the Public Switched Telephone Network or Service Provider lines. Moreover, it allows internal communication for a business between users.
A PABX installation is a system that automates telephone switching within a private network. In a typical corporate setup, a company uses phone lines to handle incoming and outgoing telephone calls. In this kind of setup, the phone carrier is given the task of managing the different lines, with the different lines all leading to a multiple-line unit managed by a live operator. This particular setup allows external calls to enter the private network via a singular contact point, and it also permits extension units to communicate with one another internally.