One thing that's never been clear about Amazon's rumored 3D head-tracking smartphone is how it would rise above cheap gimmickry and actually prove useful.
By tilting the handset in different directions while the device is in use, Amazon’s interface will display additional information on the screen without the user having to touch or tap anything. This will not only be a point of differentiation for the company’s phone lineup, but also a way for larger devices such as Amazon’s upcoming 4.7-inch flagship phone to be operated more comfortably with one hand.
BGR's "trusted sources" provide some examples of how the Amazon phone could work: You might be able to tilt the phone in the Kindle app to bring up Amazon's X-Ray feature, which provides supplemental information about what you're reading. You could potentially tilt in the messaging app to bring up a panel of camera options, or tilt in the maps app to see Yelp ratings atop your search results. Even the phone's menu system could be tilt-based, letting users slide a panel of options onto the screen by twisting the phone.
The immediate concern here is that all the tilt detection would become an aggravation. You wouldn't want a bunch of menus to pop out of nowhere just because you shifted your weight.
But I very much like the idea of tilting a big phone to bring far-flung elements within reach. Larger smartphone screens are wonderful for many reasons, but do require some contortion of the hands and thumbs for one-handed use. Being able to tilt a distant button into thumb range could be just the solution that no one's thought of yet--as long as it actually works.