A telephone system and method is provided for delaying authorization validation queries until a dialed phone is answered. This way, authorization validation queries are avoided in cases where a requested phone line is busy or not answered. In a collect call scheme the system may even delay queries until...http://www.google.com.hk/patents/US5894511?utm_source=gb-gplus-share專利 US5894511 - Validation query based on a supervisory signal
