iPhone 4

The iPhone 4 was released in 2010 and discontinued in 2013 (2014 in some non-U.S. markets). Lifewire retains this article for its historical value.
Thanks to a loss of a pre-release version of the iPhone 4, and Apple's confirmation that the lost device was authentic, this model of the iPhone was revealed to the public before Apple officially announced it. Needless to say, its release was a bit anticlimactic.
That said, the iPhone 4 was a major step forward over its predecessors in a number of areas. First, the iPhone 4 was visibly different from earlier versions thanks to its more-square shape (gone were the iPhone 3GS' tapered sides), a microSIM slot on its side, and circular volume buttons on the left. When looking at the iPhone 4 it was also immediately clear that something had changed: the screen was much higher resolution. It was the first iPhone to use the Retina Display screen technology.