San Diego-based H2O Audio, a developer of waterproof headphones and other accessories, said yesterday that the firm has inked a multi-year partnership with Olympic swimmer Michael Phelps. H2O Audio said that the firm and Phelps will collaborate on product development and marketing initiatives. Financial details of the deal were not disclosed. Phelps' image and voice will be used on H2O Audio's product packaging, advertising, and displays, the firm said, with a campaign to launch in the summer.