How Office Phone Systems Work

by Jackie Lohrey, Demand Media
Office phone systems can include almost limitless incoming lines.

Office phone systems can include almost limitless incoming lines.

Hemera Technologies/ Images

Equipping your business with a phone system rather than a multitude of single-line phones can improve office communication and increase productivity. However, they can be confusing -- especially in the beginning -- as the process, as well as the phone itself is often far different from what you currently use. Although the provider, phone type and features, and the size of the system make each phone system different, basic “inner workings” share common characteristics and can give you a good starting point for better understanding an office phone system you are considering or are already using.

The Facts

Before you can understand how an office phone system works, you must identify it by type. The two basic types – multiline and private branch exchange – are similar but differ in their degree of complexity. The simplest is a standard multiline phone. With a multiline phone, you can have a maximum of about eight to 10 individual lines coming into a single phone, each of which usually displays as an individual line, such as “Line 1,” “Line 2” and “Line 3” on each phone extension in the office. Multiline phones require manual operation. A private Branch exchange system – also called a PBX system – is an automatic phone system that larger businesses often use. PBX systems give you the option for additional lines and automation makes a central receptionist unnecessary.


Multiline phones work differently depending on available options. In a basic system, each line in the system has a separate phone number. You publish each phone number and treat each as a separate line. The line receiving the call will ring and a light will blink, but if the line is in use, the caller will get a busy signal or go straight to voicemail. Another option is a service called “rollover” in which you publish only one number and incoming calls occupy lines in descending order. For example, if you have three incoming lines and two callers place a call at the same time, one call will ring on Line 1 and the second call will ring on Line 2. Both types usually offer features such as voicemail and call transferring, as well as a speaker system that allows a receptionist to alert employees to incoming calls.

PBX Basics

A PBX phone system performs the same general tasks as a multiline system but without human assistance. Incoming calls enter through a buffer, an electronic, central receiving area and then depending on the number the caller dials, one of two actions takes place. If the caller dials a central number, they will most often have the option to dial an extension number immediately or listen to an automated list of phone extensions, choose one and connect. If the caller dials one of the extension lines directly, they can bypass the system completely and connect to the extension. As an example, if a central number is 555-4123, direct extension numbers can be numbers such as 555-4124 and 555-4125.

PBX Options

An additional option PBX phone systems provide is the ability to connect internally. Employees can use a phone to dial other office extensions without using an outside line, usually by dialing the last three digits of the number, such as 124 or 125. To access an outside line and place an outgoing call, most PBX systems require that you include one additional number – such as the number 9 – before placing the call.

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