Macbook Pro & iPhone headphones

For some reason my MBP isn't recognizing my iPhone headphones. Sound just keeps on coming out the built-in speakers, and they are not showing up in the sound preferences. I tried another pair of headphone and they work just fine. I also tried using them on my iPod and iPhone and they work just fine there, so I'm not quite sure what the problem is. Any help would be greatly appreciated.

Message was edited by: natelock