Possible answers, all valid, all tell you absolutely nothing
* I'd change nothing, it works "AS A PHONE' just fine. There are better things to to work on
* I'd attach it to the side of a rocket so you could use it as a handle. I'd much rather ride a rocket than use the phone
* I'd double the speakers and mic and offset them at 45 degrees so two people could hug cheeks while talking to the same person
* I'd give it a display, add a computer, and have it pocket size and it would annoy you all day long with notifications and distract you from getting anything done. People would stop using it as a phone and mostly only write text messages to each other which would be way less efficient than voice. Oh wait, you said "improve". Yea, ok, bad suggestion