Themes support is one if the major features that jailbreaking your iPhone supports. Winterboard enables you to choose an array of beautifully designed themes.
Geohot’s jailbreak for iPhone 3GS was not playing well with Winterboard. Cydia’s Saurik released a revised mobilesubstrate which enables themes support the way we are all used to!
Launch Cydia and Click in refresh. You will find mobilesubstrate. Install it, reboot your iPhone and choose a lovely theme!