Rumours of Apple getting an OLED screen upgrade have been floating around with a release from 2018, but it looks like that's not the case. According to more recent murmurings the iPhone 7S will get the first OLED display to hit an Apple smartphone.
While it doesn't look like OLED will make it to the iPhone 7, expected to appear later this summer, it should be hot on its heels in the iPhone 7S release later next year, according to Chinese site Nikkei.
Currently Apple uses IPS LCD displays in its iPhones. Upgrading to OLED will mean it can make thinner and more flexible displays which are also able to be more power efficient. On top of that OLED can display better blacks and richer colours than LCD. It's good all round and has already appeared in the Apple Watch.
The delay from Apple has likely been thanks to competitors LG and Samsung being the main manufacturers of OLED displays. Apple is reportedly near to closing a $12 billion deal with the two companies for mass production of these OLED screens.
Apart from all the advantages mentioned above, the OLED could allow Apple to create a more flexible phone and also offer an always-on display for at-a-glance notifications, without chewing up power. Even if this simply offers better iPhone battery life it'll be worth it.
Expect the iPhone 7S to appear around September 2017.