It is interesting to see Amazon enter the ring with Google and Apple on the phones and music market. A few years ago I don't think I would have entirely believed it. But I guess that's why I don't do any investing outside of index funds!
What kind of monthly mobile data usage will this application entail? iTunes is geared toward the model of "download, then listen on the go" with the option of cellular streaming. Amazon Music seems the reverse, geared toward cellular streaming, with some caching. The service certainly provides the phone with the feature of free mobile music, but at the cost ($?) of significantly increased consumption of one's data plan.