Three day old phone and it seems I have purchased a bag of nails
I see dozens of people with the same problem and all with no permanent fixes. It's obvious Nokia is aware but by their silence on any forums, including their own, nothing is being acknowledged or what they intend to do. For me the phone goes back for a refund and Nokia should withdraw the model until a hardware fix is put in place. There is no customer care on this topic and I hope Watchdog take up the issue
Experiencing this also. I can't do anything on the call. Have to wait for the other person to end the call because I can't access phone controls.
Wanted to add that I was able to get out of the black screen by pressing the power button which locks the phone but the screen at least shows up again.
Got another call and was able to experiment. I got rid of the black screen by using the fingerprint sensor so that's another way to do it.