Business telephone systems are multiple line telephone systems utilized in business environments. They could be main systems for small scale operations or hybrid systems; or PBX (Private Branch Exchange) systems that are meant for large scale operations or the more recent VoIP systems.

In a key system, a central user can look at and control calls directly and manually with the use of lighted line buttons. The operations of PBX are comparable to the usual public telephone system. In this system, the calls are automatically connected to the dialed numbers. PBX systems are also referred to as PABX (Private Automatic Branch Exchange) and EPABX (Electronic Private Automatic Branch Exchange). They are in general employed when an office or business needs a dedicated telephone exchange. PBXs share the same technology as that of the central office telephone systems.

Some complex and large PBXs have more capability and features when compared to public systems. Private Branch Exchanges allow interconnections between internal telephones, faxes and modems and so on, to form a telephone network. Extension is a term used to describe the end points in a network. PBX also links into the PSTN (Public Switched Telephone Network) so as to allow outside calls into the organization which further reach the required desk via the extension numbers. Hybrid systems combine the characteristics from the Key system as well as the PBX system.

More on business telephone systems.