Key system

A key telephone system is a business phone system that lets users access several lines; make, place, transfer and conference calls; and more. Some key systems have integrated voice mail. Some have Automatic Call Distribution (ACD) capabilities. What were once electro-mechanical clunkers are now sophisticated, digital systems offering most or all of the power of large PBXs (including computer telephony integration) but in a smaller package.

By traditional definition, key systems are not switches (e.g., they lack the ability to perform functions traditionally assigned to PBXs such as selecting paths or circuits to route calls over random trunks). Traditionally, key systems have been configured square, meaning that all outside lines (trunks) show up on every phone, and a user must manually press the button on the telephone to select a specific CO line to engage. Today, however, a good portion of products, under FCC specifications, fall into categories of both key system and PBX, hence the birth of a beast called the hybrid non-square systems that serve multiple trunks and connect to a mix of digital station-sets and analog phone equipment, just like a PBX.

Other phone systems pack plenty of features, but don t have a Key Service Unit (KSU the cabinet that contains all the switching electronics of larger systems). These so-called KSU-less systems are bringing big phone system power to the Small Office/Home Office (SOHO) market.

The first question a prospective buyer usually asks about a key system is: How many lines and...