As a matter of fact, it's the 802.11g/Bluetooth combo chip that also has an FM tuner (and possibly a transmitter) built-in.
However, there has been no evidence to date to suggest that the necessary internal antenna connections have been made in the iPhone which would be needed to allow that hardware to actually work.
They actually went with the BCM4325 which only has a FM receiver on it. It was rumor before hand that they would put the 4329 in it. As lines in code referenced it.
http://www.phonewreck.com/2009/06/19/iphone-3gs-teardown-and-analysis/