So says this Newsfactor article. Snippets:
At the same time, the music-downloading business itself is in flux. Apple's iTunes service remains solidly attached to its per-track pricing model. Competitors, on the other hand, are trying new business models that combine per-track pricing with monthly subscription fees for unlimited listening.
In addition, the digital rights management scheme used by iTunes differs from that used by Windows Media Player, which can present complications for consumers and service providers.
All this makes releasing service-specific mobile handsets a dicey business. It is no wonder that the manufacturers and service providers are hesitant to announce media partnerships so quickly.