You can change the Phone app dial pad buttons shape in iOS 9 with new free Cydia release known as PhoneDialReformer if you are jailbroken and haven't upgraded to iOS 10.0.2 update. You can use this tweak to play with the roundness and corner radius of the dial pad buttons to make them look unique.
How To Change The Look Of Phone App Dial Pad Buttons On iOS 9
To get the ability to reshape the Phone app dial pad buttons shape on iOS 9 iPhone head to Cydia’s BigBoss repository and download the tweak absolutely for free. As the tweak requires the Phone app, this will not work on the iPod touch or iPad. Once PhoneDialReformer is installed, you can launch the Settings app and open the tweak’s preferences pane:
Here you'll find a lot of configuration options. There’s just a toggle switch to turn on/off the tweak on demand, as well as a slider to adjust the amount you want to reform the buttons by.
You can use the slider to choose a value between 0 and 25. As you move the slider, it changes the shape and corner radius of the dial pad buttons. So you can set them to match your own tastes. there is no need to respring your device as all your changes will take the immediate effect. Nevertheless, it is recommended to close and re-opening the Phone app any time you make changes for the best results.
The effects are only aesthetic, so you can still use the dial pad in exactly the same way you’ve been using it even before using the tweak. If you’re into themes, changing the Phone app dial pad buttons shape in iOS 9 Phone with DialReformer tweak could help you to get the unique look you’re going for to better match your iPhone’s theme.