O.J. Mayo says he has decided to exercise his option to become a free agent this summer, with a goal of working out a longterm deal with Mavs. Mayo says he reached that decision after meeting today with Rick Carlisle and Donnie Nelson. He says they told him they want him back. Mayo signed a two-year contract with the Mavericks last summer and had the choice of whether to return at a $4.2 million salary or declare for free agency. "I'd like to be back next year," Mayo said