It’s called the Elasty and it was designed by Yoori Koo and it even won the Korean Belkin Design Awards. It’s basically an iPhone 4 case with 5 slits at the back that are made out what appears to be rubber/stretchable material. When the slits are pulled back, as the photo above demonstrates, you can tuck a variety of objects behind it – earphone cables come to mind.
There are probably plenty of other uses for it too such as tucking dollar bills, post-it notes when going grocery shopping, a pen, credit card, driver’s license, etc. Granted it does not look like it will do a very good job of protecting the back of your iPhone 4, but it’s pretty interesting to see a case that has been designed to go beyond the typical expectations that come from a phone casing.