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.
TelecoTech has the operation to provide hosted VoIP services and is a reseller and technical support and consultant company for various brand name VoIP providers.