A Private Automatic Branch Exchange is known as a PABX. It is a phone system that enables companies to make internal calls as well as out-of-office calls. It is a private branch exchange that uses a single central switchboard to connect lines from various locations or businesses. Additionally, it can be utilised for intercom use, allowing staff members to communicate without utilising the main switchboard. It is usually installed in an office or business, enabling users to receive and make voice calls on their desk phones and office phones. In addition, it offers voicemail, call parking, call forwarding, and other features that are typically not found on regular phones. With the help of an analogue switch, users can configure the single telephone line—which is shared by all users on the same network—to function as either an analogue or digital line for making and receiving calls.