Abstract: A method for use in an electronic switching system having more than one operator position system connected thereto, is used for wiretapping in order to determine a time length of a telephone call between a caller and a receiver. The method comprises the steps of: (a) measuring an elapsed time from the instant the caller is connected to the receiver; (b) checking if the elapsed time reaches a preset time; (c) wiretapping when the elapsed time reaches the preset time; (d) resetting the elapsed time and going back to step (a) if the caller is determined to be still on the line by the wiretapping; and (e) releasing the connection between the caller and the receiver if the caller is determined not to be on the line any longer by the wiretapping.