In the jailbreak community, there are plenty of ways to change the way that your iPhone interface looks. Icons especially are a large part of the iOS interface that people like to tweak to their liking.
Once jailbroken, you can do all kinds of things to your iPhone's icons. You can convert old app icons to retina display icons, arrange the way they look on your home screen in any way you want, and the list goes on and on.
Themes via apps like WinterBoard also allow you to change your icons to suit different looks. IconHarvester, by NanoTech, is a relatively unknown jailbreak app that focuses specifically on icon-theming. It's elegant and simple interface make it well worth the price for any icon lover...