A large scale voice store forward system has been developed for NTT's ISDN, the Information Network System (INS). This system, which is based on digital signal processing (DSP), offers message delivery, message board and information proffer services, and it has user-friendly advanced features. Single chip DSP LSI are utilized for voice code conversion with pause-in-speech detection and DTMF reception, and a new backward-hangover processing technique has been introduced for pause-in-speech deletion. The field trial showed that the system performed as designed, that the user-friendly features truely helped the user to use it easily, and that the amount of storage used was reduced to 35% by adopting adaptive differential PCM coding and pause-in-speech deletion without voice quality degradation. The system was improved to meet network requirements, and commercial service was started in November 1986.