Leonardo "Titanic" DiCaprio joins the ranks of U.S. stars appearing in Japanese TV commercials, in two spots introducing DDI Cellular's new digital phone system. In the commercials -- directed by Meiert Avis and produced by Windmill Lane Productions, Santa Monica, Calif. -- a workbound Mr. DiCaprio uses the phone to talk to his girlfriend. Asatsu, Tokyo, handles. Senior creative director: Makoto Eguchi. Art director: Yoichi Komatsu.