Apple didn't come up with a new design for the smaller iPhone SE. Instead, they've reused the old iPhone 5s with new internals. It's an odd move, which we witness for the first time - it's like reusing the same looks of a phone model third generation in a row. And that from the company, that practically invented the two-year phone redesign cycle.
Source: http://www.gsmarena.com/apple_iphone_se-review-1424.php
