... extensions. 2. Busy Tone Detection for Incoming Calls System can detect busy tone of CO lines being occupied by an incoming ... charge, you can set class of service for extensions, account codes andCO-to-CO passwords, for Long-distance Call, Local Call, Intercom and ... and Outside Line FSK and DTMF is available for Co. Line, but only DTMF for Extension Line. Information of 50group incoming call numbers ...