A telephone test and assignment bureau is provided with a telephone instrument interconnected with an automatic wire pair identification field unit. A telephone number to be verified is dialed on the instrument and a start button is illuminated when the connection is completed by the switching equipment....http://www.google.com.hk/patents/US3973090?utm_source=gb-gplus-share專利 US3973090 - Telephone number assignment record verification apparatus and method
