My most important item on my bucket list is creating a phone which runs a custom OS and sell it to the public. Of course this a life goal and I would not want to rival the iPhone or Android, it would be something totally different. Something like MVMT watches. They do not rival Rolex or Patek Philippe, they are doing their own thing. And they are doing it right because I just ordered one!
I definitely know that my OS would only have a few functions but it would be good at everything else. Great camera, great screen and great battery life. The OS would be fast and snappy like Windows Phone and be totally different from the whole idea of having icons for the apps. I am not even sure it would have an App Store, probably not.
But the phones would be manufactured and designed by us, like the Google Nexus is designed by Google. I think one of the most important aspects of user experience on a mobile device is the feel of the actual device in your hand.
So.. I would definitely start the design process by 3d printing dummy phones. I would hand them to people around the whole globe and ask their opinion about the feel of the device in their hand, after concluding the results the perfect phone shape could be designed. For example I strongly believe that phones should not have any bevels around the screen, but only a thin one which is a little higher than the whole screen. Why? Because if you drop your phone face-down , it won’t brake. Also, I think after a given size, making the phone thinner is actually worse than leaving it as is because users will have a hard time holding it in their hand.