Telephone Systems Telephone systems consist of three primary components:
Telephone Service: This is the dial tone that you get from your telephone company. You pay a monthly bill for the telephone company to route calls to you and to allow you to make outbound calls. Traditional telephone service is provided using analog lines and digital lines (T1 and PRI) while VoIP service is delivered over the Internet.
Telephone Sets: These are the devices that employees use to carry on conversations. They usually sit on an employees desk, and they can be analog, digital, or IP. Modern designs also allow cell phones to be incorporated into the business telephone system.
Telephone Switch: Commonly called a key system or a PBX, this is the equipment that sits between the telephone sets and the telephone service. It provides call routing, and it converts signals between the telephone company and the telephone sets to allow interoperability. Messaging may be included "in skin" or externally.