Key systems and PBX systems are the two most common choices for businesses in terms of enterprise telephone systems.
Key systems only require the installation of new compatible telephone sets. A key system unit, which can be a separate box or an attendant’s phone, controls the system. Many buttons or keys are installed on the phone, representing direct access to individual lines. Users press the corresponding key to call a specific line and that’s it. The relevant button lights up to indicate that the line is in use. Basic popular features such as music-on-hold, privacy, speakerphones, paging, intercoms, lights, hold are supported.
A PBX or private branch exchange system is a vastly more complicated and feature-rich affair. PBX systems connect enterprise “trunk” lines with individual user lines on one end, and to the rest of the world on the other end. It acts as a central switching station. All incoming and outgoing calls are controlled by the PBX system, and routed to and from the enterprise’s extensions.
Contrary to key systems, PBX systems allow enterprises to have more extensions or phones within the enterprise networks, than outside lines. Hundreds of lines and thousands of extensions can be supported. PBX phone systems require the installation of specific hardware like a PBX system which is basically a computer with specific software installed controlling the enterprise network. They are therefore more expensive but can easily scaled when needed.
Key systems are therefore more suited for businesses with less than 30 or 50 users, and PBX systems for larger businesses.