This arrangement allows the system to offer many features, since the KSU can monitor the status and needs of each phone. The disadvantage of this arrangement is that the KSU requires professional installation, raising the cost and complexity of the system. Some systems require additional wiring to provide all features. As you might have already deduced, KSU-less phone systems do not require a central cabinet. Instead, each telephone contains the circuitry necessary to offer various features.
Installation can simply be a matter of installing the phones into existing phone jacks.
A side benefit of such an installation is that KSU-less phones do not require the costly wiring of more advanced phone systems. These phones can easily be unplugged and moved to a new location, or sold. This flexibility allows you to treat a KSU-less system much like any other business machine, rather than as a permanent investment in your premises. An additional advantage of KSU-less systems is reduced vulnerability to equipment problems. With a key system, KSU failure will cause systemwide disruption in the company's telecommunications.