STOLEN NUMBERS -- [New York Times, p. 31, 7/5.] Federal investigators said the scam was ingenious in its simplicity: Five people in New York City would tap into public pay phones at major airports across the country, then steal calling-card numbers punched in by unsuspecting travelers. The scheme ended last month with the arrests of four men and one woman. But the case is only the latest machination in a $4-billion-a-year telephone fraud industry that keeps reinventing itself. "This is something we have not seen before," said Boyd Jackson [of] network security at AT&T, one of the industry experts who helped Federal investigators on the case. "And there is nothing I am aware of that customers can do to fully protect themselves." The Secret Service was tipped off by AT&T, Bell Atlantic and MCI after they received an unusually high number of complaints from customers who had recently used their calling cards in airports. [Also San Jose Mercury News, 1C; Rocky Mountain News, 33A; Sun-Sentinel, 3A, 7/4.]