The Apple iPhone comes with a set of stereo earbud headsets, which is not something you want to use when driving a car. You cannot have headphones in both ears when driving a car for safety reasons.
And leaving one earbud hanging just looks stupid, and it gets in the way, swinging around.
This mono headset from Cellet is a much better solution. It works with my iPhone 3G perfectly. Audio is loud and clear, and the mic picks up my voice no problems from where it hangs near my lapel.
I didn't want a relatively big, bulky Bluetooth dongle hanging off my ear, and this Cellet headset is MUCH smaller. I highly recommend this Cellet headset to anyone with an iPhone.