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.
Stonehenge is an international carriers carrier offer a full A-Z, US domestic and Canada termination, turn key white label VoIP solution, Mobile VoIp, and ratail IP products.