The communication system thereof comprises an elevator car extension telephone, a machine room extension telephone, a car top extension telephone and a pit extension telephone. Each extension telephone is interconnected with dependent office isolator. A call button is set on the elevator car extension telephone; the call button of the elevator car extension telephone is connected to a radio gateway through the dependent office isolator and is seamlessly connected to the radio network through the radio gateway in order t build voice call connection. The invention is an improved solution on thePatent No 2005 100119195.5.