This bluetooth adaptor works very well with my iPhone 3GS, the only thing that does not work is the track FF & REW funtion, this is down to the iphone not supporting bluetooth remote profile, hopefully this will come in the next OS update.
The sound quality is amazing. According to bluetooth tech specs, on paper the sound quality should be inferior to the wired method however with my ears the sound is identical for quality and loudness. I have connected my Shure SE530 short wire, Sennheiser HD 25's and the Bose QC 3 to the 205's and I cannot detect any sound degradation at all however, I'm not an audiophile expert.
The battery is very good, lets put it this way, the battery on my 3GS with bluetooth on ran out before the SE 205. This is the only downside to BT headphones, the wireless convenience will drain your phone's battery however I believe it's worth it for the freedom of wireless.
I am very careful with all my headphones but I have caught and torn the wire of various pairs on door handles , clothes and in crowds on the tube causing loss of sound in one or both channels but with BT this is a thing of the past.
I have used the SE 205 in the gym and it's so good not having my iphone in my pocket weighing my leg down or falling out while on the rower OR OTHER Machines, now I just leave my iphone on the floor while I work out and stretch. You may think this is no big deal and iI am being OTT but trust me it makes a big difference.
Overall these get 5 stars. I was going to buy the Sennheiser MM450 and one day I probably will (tried them in selfridges and they are amazing and with zero wires) but these stopped me and will do more than the job of wirefree music listening for now.