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.
The Center of the System Administration was founded in 2001, in order to satisfy the needs for IT services of small-to-medium scale organizations by providing Open Source Software solutions.