I think a side button, like the one on Apple Watch, could make a lot of sense for the iPhone. The paradigm of having a screen full of app icons hasn't changed since the original iPhone. Microsoft took it in a different direction by having tiles that give you more information about people on the home screen. The Apple Watch has it both ways, with a home screen of apps, along with its people view. I think the people view would make sense for the iPhone as currently making phone calls is one of the more cumbersome tasks on the iPhone (unless using Siri). Apple could even allow third party apps to integrate with a People view. You select a person and then choose built-in functions such as Call, Message, E-mail, FaceTime, but also things like send Dropbox attachment, etc. Apple tried this a bit with iOS 8 in showing recent and favorite people in the App Switcher, but I don't think the placement is great. It's at the very top of the screen, and there's too much going on. I could see Apple adding a button to the right side of the iPhone for this purpose. It brings it back to being a phone again, which is the area Apple has probably innovated the least since the original iPhone.