PABX (Private Automatic Branch Exchange): an automatic switch which includes extensions and trunks used to communicate with the outside. Each extension has a separate phone number used to communicate with each other and the switchboard also provides a code for the extension to call out.

The PABX switchboard has a capacity from 4 internal extensions to several hundred internal extensions, using trunk lines which are phone numbers provided by the Post Office.

The telephone switchboard system provides subscriber machines for connections to departments and connections to subscriber lines of telecommunications service providers. The use of the Switchboard brings conveniences such as: using a few subscriber lines from the Post Office, significantly reducing costs in registering new subscribers from the Post Office, exchanging information between departments in the company without paying costs, providing a landline contact on multiple extensions to conmunicate with customers through a single number.