Amazon already offers “Songza”, which lets users create their own custom radio station and then share it with friends. Now CNET says Amazon is buying “indie-music download service Amie Street” and will use it to “bolster the content available for Songza.” Current subscribers to Amie Street were notified this morning that the company had been acquired by Amazon. They’ll need to pay extra attention, because they must download the Amie Street music they've paid for by September 22. To help ease the change, they get a $5 gift certificate to Amazon’s MP3 store. Amazon has branched out far beyond books and Kindles, selling everything from music to shoes. More than half its revenue is now believed to come from non-book categories.