I was searching about how to add a slider of my choice and couldn't find anything. How do I do this?
Whatever the theme that you're using is, there should be a bundle folder in there. In that folder should be another folder called com.Apple.TelephonyUI. In that folder are the png's you need to replace. If you have another slider you'd like to use instead of the one you have now, delete the pngs that are currently in your theme and the put the pngs of the slider you want to use in that TelephonyUI folder. Respring and your new slider should show up.