Good old rotary-style pay phones are making a comeback. The reason is not nostalgia but an effort to thwart drug dealers who use push-button phones as their command posts. The dealers, who typically wear pagers, can send and receive messages via touch-tone phones to clients and colleagues. But most pagers will not work in conjunction with dial phones. U S West Communications, a subsidiary of one of the regional phone companies, has replaced push-button pay phones with rotary models at 18 locations in the Minneapolis-St. Paul area. Neighbors and law-enforcement officials are delighted. "The rotary phones have stopped the drug traffic. We feel a lot safer," says Billie Curren, 58, who headed a neighborhood group that first complained to the telephone company about the problem.