Headphones allow you to listen to music from your iphone 3g device and if your iphone 3g device and headphones support A2DP then you can use the same headphone for iphone 3g device calls. Most common types of headphones are in-ear ear buds other there are other types as well including on-ear headphones that stay on your ear or around-ear headphones that form some sort of a suction around your ear. In addition to wired headphones there are Bluetooth headphones that are without wires.
