How to play music from my iPhone through the stereo in my Fiat 500 Lounge?

I have recently bought a Fiat 500 Lounge, which has a windows USB port instead an AUX port. Is there an adapter that I'm able to buy so that I can play music from my iPhone through my car stereo? Any links on where to buy decent adapters would be helpful.

A bit on the pricey side but try the 'blue&me adaptor' (http://www.fiat-accessories.com/blue-and-me-adaptor-for-iphone-and-ipod)