Some telephones, depending on the brand and model, have the intercom function, which allows to begin communication by sending the signal. When the signal comes, the telephone set rings a signal different from the standard ring tone call. After that the telephone temporarily switches off from the telephone line and works as an intercom.
Code-A is Telecode Communications Inc. billing for collecting CDRs and Softswitch management via TXT files, SNMP and DBMS. Code-A has its own framework designed to calculate every call and not to miss any.