Dual channel bluetooth headset for iphone 3gs

i am trying to find out if anyone has information regarding bluetooth headsets in terms of being able to listen to music thru them, and also phone calls--the wired headphones that come with the 3gs, have button which allows volume control and to answer and make voice activ calls; do any of the bluetooth headsets do same or similar? also, is it better to have single ear or both ear headset in this case?