One of the Z9 techs told me that it is designed to turn off when you plug it in to the charger. He said you can't use it while it's plugged in anyway, but had no answer when I said it's stoopid to have to turn it back on when someone calls while it's charging.
That said, I just remember to turn it back on as soon as I plug it in, and that works.
BTW, it will work when it's plugged in (and turned on), if you can stand the charging plug hanging from your ear.
Over all, the sound is great, but I did have some problems such as when wearing the headset on my right ear and the phone on my left hip, it loses the BT connection while walking, and I get a lot of static when it does stay connected.
I have gone back to my Plantronics 510 mainly because it's much easier to switch back and forth between my PPC-6800 and my work cell phone. I bought mine off eBay, so I probably can't return it. I could be persuaded to sell it, if the price is right.