A method and apparatus for telephone call answer supervision, capable of detecting the completion of both national and international calls, which employ different answer confirmation formats, and provide confirmation that a placed call has been answered if least one of the following conditions occurs:...http://www.google.de/patents/US5134651?utm_source=gb-gplus-sharePatent US5134651 - Method and apparatus for providing answer supervision and an autonomous pay telephone incorporating the same
Method and apparatus for providing answer supervision and an autonomous pay ...
