Tokyo - Sony has partnered with KDDI, Japan's second-largest mobile network operator, on a new mobile music service that lets users transfer songs from their handsets to other portable music players. The au x Sony Music Project, slated for launch in December, will let users of KDDI's EZ Chaku-Uta Full music download service to transfer tracks to digital Walkman players, as well as transfer songs ripped from CDs to their mobile phones.