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.
Provide wholesale international callback service in China for voip service providers and call shops. We offer competitive price and billing system to our wholeseller. We are using SS7 PSTN line and no connection fee to customers.