The earphones that came with my Xperia X10 have a small silver button. When the headphones are plugged into my phone pressing it does nothing - the earphones sound fine but no change when the button is pressed. My wife has a Sony MP3 player which is a couple of years old, sorry it don't know the model - however I was loading some songs on it for her and I grabbed the headphones from my X10 and plugged them in. The sound from the MP3 player through the headphones was washed out and flat until I pushed the silver button at which point the sound filled out and sounded great. The only problem is that to keep the good sound you had to keep the silver button pressed in,, not very practical. So my question is,, what gives with the button on the headphones that came with my phone?? Thanks.