System and method therefor of preventing fraud on pay phone credit/debit calling card authorization

Abstract

To prevent fraud perpetrators from using a public pay telephone to illicitly collect account numbers, authorization codes or personal identification numbers from an unsuspecting user of the telephone, the instant invention disables the keypad of the telephone if an incoming call is being received at the time that the handset is lifted from the phone by the user. In one method, the ringing signal and the off-hook condition are detected and a control output is provided which disengages the dialing tone generating circuits of the telephone until the handset is placed back on-hook. According to an alternative method, after the handset is lifted, a dial tone is sensed and evaluated by a dial tone discriminator to determine whether the dial tone is likely to be a valid dial tone from a legitimate service provider. If the dial tone is determined to be invalid, then the keypad of the telephone is disabled until the handset is placed back on-hook.