Rumours have been going around for more than a year now that Amazon is working to enter the smartphone market with a Kindle-branded handset. Now, the Wall Street Journal is reporting that the tech giant is actually working on two phones — one of which will have a 3D screen.The Journal reported late last week that Amazon is “developing a wide-ranging line-up of gadgets” including the two phones. Citing multiple anonymous sources, the Journal says the 3D-capable smartphone will not require special glasses and will use eye-tracking technology powered by the front-facing camera — allowing users to navigate just by moving their eyes.The navigation system sounds remarkably similar to that used by Samsung on its recently-launched Galaxy S4 Android smartphone, which gives users the ability to scroll web pages, books and other digital content simply using your eyes.None of the technology described by the WSJ is particularly new. As well as the eye-tracking technology launched with the Galaxy S4, the glasses-free smartphone revolution began with the LG Optimus 3D and all-but ended with the HTC Evo 3D, the market having decided that the 3D displays fitted to both smartphones were little more than a gimmick that didn't really add to the user experience.While it's not particularly surprising to hear about Amazon working on a smartphone, it is a bit strange to hear news of a possible 3D-enabled device. Despite a fair amount of hype a couple years ago, 3D technology has had mixed success at best in the consumer technology market.Amazon itself has plenty of experience in making smartphone-like devices. It’s Kindle family of eReaders include models with integrated 3G connectivity, used to allow the owner to browse the Kindle Store and download books, magazines and newspapers even while away from a Wi-Fi connection. Its Kindle Fire range of tablets, based on a heavily customised version of Google's Android platform, give the company further experience in the technology required to build a smartphone.In addition to the two smartphones, Amazon is also said to be working on a device for streaming music and a set-top box, the latter of which was also reported by Bloomberg BusinessWeek last month.Amazon, for its part, has refused to comment on the rumour, but given the aggressive pricing of its tablet products it seems likely that it will be pricing the Kindle Phone to sell — possibly reigniting the trend for 3D-capable smartphones.