Great to find a product that actually does the job but a shame it's missing features.
Battery life is about a day for leaving it on for voice calls, about half a day if your occassionally listening to music and 2 hours if your listening to music constantly.
I have found that intermittantly it will loose connection and music will cut out.
My only other issues are that the volume control is a little hit or miss, you hold down the Play button and have to listen to the volume level as it lowers and then rises. If you stop to early and its not loud enough you need to repeat the procedure. Also it would be nice if you could lock the buttons, several times the Call Answer/Redial button has been pressed by rubbing against clothing and cut out the music and started to call someone. You cannot change tracks with this device.
This has been tested successfully with Sony Ericsson k800i and the iPhone 3GS (Any iPhone with Software 3.0 or above will now play music with this device). Make sure you device has A2DP on it for Stereo Bluetooth, otherwise this will be a mono Hands free device only.