The system only works in North America if the emergency telephone number 911 is called. Calls made to other telephone numbers, even though they may be listed as an emergency telephone number may not permit this feature to function correctly.
There is special privacy legislation that permits emergency responders to obtain the caller's information. Even though the caller's number may be blocked for caller ID purposes, the callers details will be provided to the emergency services.
A second phase of Enhanced 911 service is to allow a wireless or mobile telephone to be located geographically using some form of radio triangulation from the cellular radio network or by using a Global Positioning System built into the phone itself. There are also other proposed features that are intended to allow telephone callers from large corporate telephone networks to be located down to the specific office on a particular floor of a building.
In all cases, the location information provided is normally integrated into emergency dispatch centre's Computer-Assisted Dispatch or CAD system, to provide the dispatcher with an on screen street map that highlights the callers position and the nearest available emergency responders.