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.
LEAD TELECOM is a wholesale VoIP carrier incorporated in Miami (Florida), with headquarters in the state of Florida, and collocation facilities in New York – EQUINIX and Miami - NAP