Sisters Venus and Serena Williams have signed a three-year marketing agreement with Canadian telecommunications company Nortel Networks. The Williams sisters, who won the doubles gold medal in the Olympics, will make personal appearances for the Internet and communications company that specializes in fiber-optics. The company is based in Brampton, Ontario, near Toronto. “Serena and I are really encouraged by what we can do with a company at the heart of the Internet revolution like Nortel Networks as we try to take the game of tennis out to kids who might not have been exposed to it,” Venus said. Venus Williams is the world’s No. 3 ranked player and also captured the gold medal in singles. She is the reigning Wimbledon and U.S. Open champion. The sisters have won three Grand Slam doubles titles.