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.
Beijing Sinoco Information Technology,Inc
Sinoco Information Technology Co.,ltd. is a high-tech enterprise committing itself to the manufacture of the VOIP terminal units
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