What is an Extension Number?
In the world of business telephony, an extension number refers to an internal telephone line (and it’s phone number) assigned to a terminal (endpoint) that is connected to the phone system or PBX (Private Branch Exchange) and allows for the communication between internal users with the minimum of fuss and a no or low cost.
To keep things clear and simple, at pascom we refer to this number as a user’s internal extension number.
Since the VoIP, the IP PBX and cloud communications have become mainstream for businesses worldwide, calling internal user extension numbers is normally free and therefore greatly reduces telephony costs, particularly for organisations that have multiple locations. All internal users need to do is dial the interal externsion number of the party they wish to call and the call is then transmitted via the IP network (i.e. company Intranet or the Internet).
Thanks to VoIP, it is even possible to connect remote workers and their telephones and configure these telephones to appear as it they are part of the phone system and to make and receive calls using their extension number. This set up is often referred to as an off-premises extension and refers to the device itself as opposed to the internal extension number. However, this practice is no longer very common and thanks to desktop and mobile VoIP and UCC apps, not really needed any more.