I have an old Grandstream VOIP phone I inherited a while back (with 3 more in the loft, so not a worry).
Not used a great deal, but it lives on my desk.
Just a few minutes ago, the LCD backlight came on (thus catching my eye) and it did a reboot - it does this sometimes.
However this time, something wasn't right, and it just seemed to loop ... rebooting all the time.
I unplugged it (9V input) left it a few minutes, and now, when you plug it in , all the lights come on, and the screen is blank. If it isn't kaput, it's doing a very good impression.
Not often you actually see something fail in real time. Not sure if that's a good or a bad thing.