Essentially there are three different types of PBX Systems.

The Analogue PBX System

The Analogue PBX System is the older style of PBX.  An Analog PBX sends the voice information as actual analogue sounds.  The information is sent as is and never gets changed in any way.

Digital PBX Systems

A Digital PBX essentially takes analogue sound and converts it in to a digital format.

Digital PBX’s will typically encode the voice using the industry standard G.711 codec.  Once the voice has been encoded, the information is sent using what is know as circuit switching.  If you use Microsoft Exchange‘s Unified Messaging you will need to have a VOIP gateway to connect it to the system.

IP PBX (Voip PBX)

An IP PBX system is what is mainly known as a VOIP system (Voice over IP).  The IP PBX will convert the voice in to data and transfer it across the network as packets.  The voice packets are sent via a method known as packet switching which is a known technique for allowing a single network channel to handle multiple calls.

Hybrid PBX Systems

A Hybrid system is a combination of a Digital and IP PBX systems.  These types of business phone systems are very popular currently as they allow organisations to transition to the emerging IP PBX systems whilst still retaining all the functionality of the digital PBX System.