Amazon is in advanced talks with the four global music companies about <A HREF="http://online.wsj.com/public/article/SB114005222162375368.html">a digital-music service</A> with a range of features designed to set it apart from Apples iTunes. Among them: Amazon-branded portable music players, designed and built for the retailer, and a subscription service that would deeply discount and preload those devices with songs, not unlike mobile phones that are included with subscription plans as part of the deal. Music executives privately welcome Amazon's plans, which they see as one of the only credible challenges to Apple's hegemony in both digital music and portable players. The service could be launched as soon as this summer.