A device for responsively providing, in cooperative association with the 911 emergency system, the number and location of a telephone, especially a PBX extension telephone, from which such a 911 emergency call originates. A first device is installed between PBXs and the extensions thereof, with the number and location of each extension stored in the device's electronic memory. A second such device is installed at a Public Safety Answering Point. When 911 is dialed from an extension telephone of a PBX equipped with a device of the present invention, even if the extension receiver is still on-hook, the extension is connected over telephone lines to the second device installed at the PSAP. The device at the PSAP then interrogates the device at the PBX which responsively transmits the location of the extension telephone from which the call originated. The device installed at the PSAP relays the location information to at least one computer which informs an operator of the location of the calling phone. The Public Safety Answering Point operator is then able to dispatch assistance to the person placing the emergency call. Provision is made for automatically selecting an alternate route if no interrogating signal is detected.