In the past, when you call an office building or business, you would either be transferred to the department you want to talk to, or given their extension number. This extension is usually a 2-3 digit code that when dialed, transfers you automatically to the particular person or department you want to speak with. The reason why this code works is because it is programmed into a PBX system.
IDC projected over 9 billion minutes of voice traffic to travel over worldwide packet networks in 2000, exceeding 135 billion minutes in 2004. Service revenue is projected at 1.6 billion in 2000 and 18.7 billion in 2004.