Curved Body iPhone 6 Concept

Curved Body iPhone 6 Concept - Similar to the idea above. The back body is slighly curved for a better grip.

But the front display is flat.

I think it would be similar to the feel of holding a sliced mango. 

Source: http://www.technologeek.net/the-iphone-6-screen-and-design-concepts-reason-for-delay/