A Office PBX or PABX system is a device that sits in between the telephone lines coming in from the service provider and the telephone handsets on the desks of each employee. In the old days, a PABX – like old computers used to be huge and extremely expensive. Thanks to the micro processor, a modern PABX is not much larger than a computer tower.Due to the reduction in size and cost of the modern PABX system, the term has started to lose distinction. In the old days there was another class of PABX that was simply called key system. Key systems typically have more advanced features and larger display handsets. This was due to the fact that the cost of the digital display handsets was very high compared to the standard analogue handsets used on many older PABX systems. Currently all systems are called “telephone systems” or simply “phone systems”. This is a generic term that could refer to any of the following terms: PBX, PABX, Telephone Switch and Key system.Due to the introduction of VoIP the traditional PABX is doomed. The bulk of the cost of a traditional PABX used to be in the hardware required to support all of the extensions which had to have dedicated circuitry to run each handset. VoIP phone systems are able to run tens of thousands of extensions from a box the size of a small computer. Obviously this reduces the cost of the hardware dramatically and it is why many corporate organisations have ditched their traditional hardware in favour a VoIP solution.Non IP PABX systems require at least one pair of copper wires for each handset. These wires run all the way from the handset in to the PABX. Power to run the handset is usually also delivered over these same wires. The PABX would simply create a bridge between these wires to the wires bringing the incoming lines in every time the phone rang or a request for an outside line was made. The early PABX systems did little more than automate the job of the telephone operator in the exchange, receiving a verbal request for a line and “patching” the call through. PABX actually stands for Private Automated Branch Exchange.