Most of the improvements that I can think of for the iPhone (and iOS apps in general) would involve removing features. An example, there is a gesture that will

Most of the improvements that I can think of for the iPhone (and iOS apps in general) would involve removing features. An example, there is a gesture that will open the camera app, I don't know what it is, but it triggers in my pocket all the time, draining the battery. I get why it's there, but most of the time it just makes things worse. I haven't used Android enough to know if it's the same issue, but the main problem is discoverability. iOS, and many apps, have a ton of features, but there isn't enough screen space to do hint to how to use them. There also isn't enough space to add more buttons. So we end up with these weird swiping motions, long press, 3D Touch or hard to hit icons. Maybe it's just me being old, but I'd recommend stripping a ton of features from phones and their apps. If you need to do anything more complicated, push people to use a device that's designed for higher levels of interaction.