Additionally, KTS are not supposed to require dialing a number to gain an outside line. On a PBX system, lines are connected to the PBX, and the PBX makes connections to the central office when the outside number is dialed.

The Key Telephone System (or KTS) is often used to refer to a simple and lower cost telephone system. Technically, a KTS is a premises telephone system that is best known by the phones having buttons that place inside calls (intercom) and buttons for placing calls outside through the public telephone network. Overall, a Key Telephone System is in the same category as a PBX (stands for private branch exchange). However, KTS rely on the telephone company while PBXs rely on a central service unit (KSU) located at the customer site. In other words, with a key system, the dial tone is generated at the telephone company central office. A full PBX generates its own dial tones.

San Diego Telephone Systems Mitel , InterTel , VOIP