Moving toward becoming a one-stop telecommunications resource, BellSouth Corp., Atlanta, has begun testing joint marketing of cellular and local telephone service in Macon, Ga. If successful, the program will be expanded to the phone company's nine-state region by the end of the year. BellSouth is the first regional Bell to offer cellular service through local telephone sales offices. Customers will have the option of getting one bill for both services. No new ad campaign is planned for the Macon test, however the news will be integrated into existing ads. Tucker Wayne, Atlanta, has the BellSouth Mobility account.