The newest 1500-mi leg off Frontier Corp.`s fiber-optic sonet network is connecting customers from San Francisco, CA, to Kansas City, MO. Coast-to-coast network availability is expected early this year, with the entire 13,000 fiber-route-mi, seven sonet-ring network scheduled for completion in 1998. The completed network is expected to have the capacity to handle 12 trillion min of traffic per month. The Rochester, NY-based corporation plans to link 100 major metropolitan cities across the country.