A voice mail service system for a private switching system includes a system matching circuit configured to couple to a private switching system and to interface all information related to a call and management of the call. By storing to-be-accessed workpieces in the buffer stations of an equipment, the operation of the facility is not interrupted when the equipment is down. If confirming normality of the encryption information, the client apparatus sets the encryption information therein. Upon completion of the first stage the protocol enters a second stage which includes the step of converging the equalizer and the timing recovery system of the master, converging the noise reduction system of the slave, freezing the timing recovery system of the slave, and resetting the noise reduction system of the master. The phase lock loop operates in a pre-lock condition to allow faster start-up.