The concepts behind many of these are patented - so to get a glimpse into the inner workings of the Apple design team, silicon.com's Nick Heath has rounded up and rated 10 of the most interesting and absurd patent applications submitted by Apple in recent years.
Many of these ideas will never see the light of day but they all either amuse or hint at what could be.
An intriguing design for an alternative iPhone, the flip device is essentially a clamshell handset with two touchscreens - one of them transparent. The patent uses the phrase "dual-sided trackpad" to describe the technology for the device. Basically, the lower half of the handset is transparent and can be folded shut over the top half, which represents the as-is iPhone display. The transparent half can be used as a touch control whether it's folded up or not.
Looking at the diagrams, the lower half is dedicated to input and the top half is given over to the display. Chances are this is one for the bin, as Steve Jobs has complained about devices which dedicate half of their physical 'real estate' to input, whether the function in focus needs it or not.
Sounds a bit complicated and pointless.
Credit: US Patent and Trademark Office