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.
Persia Telecom Co. is a subsidiary of IOEC (Iranian Offshore Engineering & Construction Company) in Islamic Republic of Iran that was established in 2004.
IOEC is the 1st Iranian general contractor in the Oil & Gas industry.