Nippon Telegraph & Telephone Corp will start offering a fixed- cost network service for computer-to-computer communications early next year and says it wants eventually to make such services its second major business area, after telephone services, which it sees becoming less profitable over time because of fierce competition The open computer network service will connect terminals and networks using routers instead of costly telephone exchange systems, enabling access to services such as the Internet and on-line computer services at lower costs than offered by existing telephone systems. Monthly charges for 128Kbps lines will be about $280 to $380, higher for faster lines. It aims for 1 million subscribers by the year 2000 but could not estimate how much investment would be needed to set the service up.