Any live application that uses such a technique?
@rckoernes, @Peter M: It has. http://theiphonewiki.com/wiki/index.php?title=BCM4325
I just wanted to know if there is any option to access it on a low-level but public way.
Actually, the iPhone 3GS' BCM4325 chip for bluetooth&wifi has FM radio capabilities. there actually is a guide that describes the basic but nobody has so far created an app (and required drivers, OS add ons, ...).