As a physician taking call while training for a half ironman this was the perfect thing to train with. I could listen to music and answer phone calls without batting an eye. This was awesome for 2 months. The buttons worked great, it was relatively comfortable, the mic was good, the volume adequate, etc. The initial problem was that I couldn't comfortably wear glasses wih it, and the second problem was that about every bit of functionality failed after some hard workouts.It started out with some pairing issues, then volume buttons not working, then the microphone completely going out, then none of the buttons working, then the bluetooth signal almost completely going out to the point where the music was choppy. I was extremely dissapointed as I have always viewed SONY as a pretty reliable company. They are reliable in that they are sending me a new one, as it has only been 5 months. My next review will follow. Maybe the other reviewers were correct and a couple of good sweats ruin it. That would be like your ipod shutting down after too much oxygen exposure.