The jailbreak community hasn't produced an FM radio for iPod Touch, which also technically has FM capability in that Broadcom chip. Just because the chip can do it doesn't mean the rest of the hardware can handle it. there has to be an antenna accessible to the FM portion of the chip, there has to be firmware support for telling the chip to switch on its FM radio, there has to be a way for the audio signal produced by the chip to be routed through the audio processor, there has to be a way to signal the chip to tune specific frequencies...I bet none of that is possible through software alone, even in a jailbreak context.