This came with the Sony Ericsson bluetooth MW600 headset which I purchased recently. The HPM-78 headset which came with it was surprisingly decent, so I decided to do a small review on it. I've been listening it to 3 days now plugged into my Samsung Galaxy S.
Build: The wires are the standard consumer fare - pretty thin but doesn't seem to entangle easily. It is meant to be used with a bluetooth headset or an extension cord, so the cable is quite short, about 35cm. It is a J-cord, not the Y-cord type. The housing is made up of plastic and the nozzles are angled with cloth mesh covering them. There is a hole above the Sony Ericsson logo which serves as a vent for the 9.2mm dynamic drivers inside. It uses normal Sony silicon sleeves.
Highs: The highs are present, but not as analytical like the Etys nor the RE0. They do not stand out, it just maintains its highs presence in the background and blends into the music very well.
Mids: Excellent mids. The mids come across as extremely natural. There is little, if any, sibilance. Nothing comes across as jarring in the mids. There are no nasal or 'boxy' vocals either. Its as if the singer is singing live and you can make out the singer's faces simply by listening to their voices.
Bass: Very low amount of mid-bass, which makes the earphones sound less "boxy" than other bass-oriented earphones. The sub bass is very strong and smooth, but can be a tad overpowering at times.
Speed: Not extremely fast nor sluggish. Probably the copious amount of low bass makes them sounds a tad sluggish.
Soundstage: Average. Decently left-right wide, but not much front and back sense of space.
Overall a very fun pair of earphones to listen to. The mids are excellent and realistic, the bass feels as if there is a nice smooth subwoofer attached to the earphones. I believe the Sony Ericsson MH-710 are using the exact some buds as well, just that the cord is longer and has a built-in mic for answering calls.