Apple offered a design change with the iPhone 3G with a full-black back but still maintaining the 3.5-inch display and the classic home button. There was also a white version for the first time ever.

The previous two models, the iPhone 3G and 3GS, had plastic backs that were contoured to fit in your palm. So it was profound to see Apple make the jump to the iPhone 4's flat glass sandwich design.

Love it or hate, the iPhone has revolutionized how we use our mobile devices. And more than a decade after its initial debut, Apple continues to tweak the formula — introducing upgraded ...