Apple has made iPhone very restricted in terms of customization, but there are ways to bypass these restrictions and install custom themes, "iPhone Hack Toolkit" is a free iPhone jail-breaking software.

Here comes good news for iPhone lover's outside USA, the so called iPhone Dev Team has released a open source fully-automatic utility named "anySim" to unlock the iPhone ready to be used on any network with all features.

This software needs to be copied over to the phone and executed, it's fully automatic, the whole process takes around 3-5 minutes :D.