BellSouth Corp. in Atlanta has launched an 18-month trial of cable-TV and video services, using hybrid fiber/coaxial-cable systems. BellSouth is delivering 56 channels of basic service, as well as options for premium channels and pay-per-view movies in Chamblee and parts of DeKalb County. These areas are currently served by Scripps Howard cable, which tried unsuccessfully to block the BellSouth trial. Scripps Howard has been upgrading its system and is ready for competition, according to Neal Fondren, the company`s business affairs director for television. Another BellSouth competitor is MediaOne, the cable-TV unit of US West and the largest in the Atlanta metropolitan area with 520,000 customers.