I'm surprised at the comment that your unable to use your own headset of choice. It was my experience with several international versions of the Sony Ericsson Walkman phones that the headset disconnects with a 3.5mm adaptor at the microphone, thus allowing you the freedom to use your earphones of choice and secondly, maintaining the mic, in case of an incomming call.
...except that really only works if your headset has an unusually short cord, like the Sony ones, which I personally did not care for. To use your own, you need to bunch up the cord using a rubber band or twist-tie. Having a wad of cord hanging next to your cheek is awfully uncomfortable, not to mention unsightly.