I have an HTC Diamond and recently downloaded Voice Command software for it.
Until I bought this headset, I was using the normal wired headset to listen to my music, but I hate wires so when I saw this device it was perfect.
When I got the headset, the first thing I did was swap the earphones as these are rubbish if you want to listen to music in high quality. I instead used my Etymotic eR6i's.
The sound quality in conjuction with my earphones was amazing, I was very surprised at this considering my music was being listened to wirelessly. Sound quality was also amazing in calls and the person on the other end could hear me perfectly. If I was listening to music and a call came in, music would be paused and when I presed the answer button I was seamlessly transferred to the call.
For me however, the problem occured at the end of the call, whether it was me or the person on the other end who hung up, when the music began playing again, it would play from the phone speakers and the headset disconnected. This wasn't a problem when no music was playing when the call came in, but this was rarely. After doing research, I discovered this happened to a lot of windows mobile users and Im assuming the headset works perfectly on most other phones, especially SE's.