Two local Nippon Telegraph and Telephone Corp. group firms said Thursday that they will launch July 17 a full-scale flat-rate Internet connection service for integrated service digital network subscribers.

NTT East Corp. and NTT West Corp. have already been offering the flat-rate service to ISDN users in limited areas in Tokyo and Osaka on an experimental basis.

The move to expand the service, which the firms regard as crucial to increasing Internet use in Japan, aims to cover roughly 50 percent of all ISDN subscribers in eastern Japan and 40 percent in western Japan, said Tetsuo Koga, executive manager of NTT East's Marketing and Development Department.