Amazon is likely experimenting with a three-dimensional user interfaces and displays to improve how users interact with its websites and apps. Because Amazon is good at working with open source code, as demonstrated by their fork of Android 4.2.2, if it is testing these advanced technologies, it is probably testing on an Android device. But Amazon is unlikely to introduce a smartphone built on these technologies anytime in the near future.
Amazon needs to drive more users to its content on the small and portable smartphone form factor devices. The company is probably testing to determine the best way to do this, be it through a smartphone or better apps for Android and iOS.
However, unless Amazon is certain that a smartphone will sell more of its digital content, it won't jump into the cut-throat competitive, low-margins smartphone business.
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