Winterboard - it's what you need to theme the iphone and change it's appearance.....

BUT FOR FUCKS SAKE DON'T ANYONE INSTALL AN APP CALLED "KATE" AS IT WILL COMPLETELY FUCK YOUR IPHONE!!!! Seen it happen many many times, so don't do it......

A lot of the important stuff will become native in 3.0 - MMS, copy + paste, etc. But there are cool little hacks available to jailbroken phones that are cool.... Just depends what you want your iphone to do really....