PABX is a business solution for companies that need many lines for in-house and outside calls .As companies grow, they need more phones to support customers, suppliers, and teams. The costs of installing and maintaining extra lines can get very high, though. A Private Automatic Branch Exchange (PABX) is a viable VoIP alternative. This system makes it possible to have many lines of access using a few connections to the public network. It allows companies to use a single access number that has several extensions. This is cheaper compared to using many landlines linked to the public network. With PABX, a company can run its own internal phone network using local extension numbers. These extensions correspond to specific phones and devices used in the corporate building. This system simplifies internal telephone communication. In-house calls don’t need to go beyond the local network. Users can also make in-house connections with the touch of a button. A PABX often greets an incoming call with a recorded message. This greeting is also called Interactive Voice Response (IVR). It usually requests a number for the caller to dial to reach the correct department or can say their commands. The PABX routes incoming calls based on the code or extension number. For outgoing calls, a PBX connects with the public telephone exchange. A traditional PBX has one or more external (trunk) lines. It has a fixed number of internal lines (extensions) connected to the trunk line. Staff and other local users need to share the external lines to make outside calls.