Key Phone System Unit

The Key System Unit (key telephone system or key phone system) is a multiline phone system that is efficient for up to a few dozen handsets. A KSU unit relies on the user to select an external line, rather than the automated exchange of Private Branch Exchange (PBX) phone systems.

ModernKey System Unit phone systems have a central hub (the key system unit) that provides functionality, such as internal calling, that non-key phone systems can’t offer. This unit – an attendant phone or separate box—that acts as controller for a limited number of lines for a limited number of extensions.

They offer convenient elements such as hold buttons, lights, intercoms, paging, speakerphones, privacy, music-on-hold, long-distance restriction, timers, and memory dialing.

Nowadays, the distinction between he largestKey System Unit and corporate-level PABX systems is increasingly blurred, with the main differentiators being the quantity, scope and sophistication of available functionality. Modern hybrid key systems are virtually  PBXs, fully digital systems that even embrace the latest VoIP technology.


  • Efficient for up to 40 employees
  • Convenience of proprietary handsets
  • Latest hybrids combine key system and digital functionality
  • Proven one-size-fits-all functionality
  • Reliability and ease of maintenance


  • Possible limitations for larger businesses
  • May lack some functionality of full-blown PBXs


Contact us today for a free evaluation, site survey and business quote.


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