Fraudulent call prevention method for multifrequency-dialling telephone station - delaying activation of microphone while called number is identified as not on exclusion list

摘要

When the handset in a public call-box is lifted, the microphone circuit is temporarily blocked by software while the first signalling tones selected by the keypad are checked by a called-number processor. The microphone is activated as soon as the number is identified as not being listed among unauthorised links. Whether subsequent signals are produced from the keypad or by an acoustic coupler is then immaterial. ADVANTAGE - Fraudulent connections obtd. by signalling from acoustic coupler are prevented at little additional expense, without obstruction of authorised toll-free calls.