Well on my second HTC One.
Last Tuesday at work I heard my phone make the restart sound which was odd because it was in a case in my pocket. It then proceeded to keep turning itself on and off every 30 seconds all while saying I had no service.
Tried all the tricks to get it working, even did a factory reset, which allowed it to assume it's final form.......a black screen with the wrong time that turned itself on and off every 30 seconds. Called up my carrier and got my new today, had to use my emergency black berry(yuck) since Tuesday since the phone doesn't use a normal SIM card, to throw into my last phone.
Considering if I should just bite the bullet and get another phone. I love this phone but it's been the most buggy experience I've ever had with a phone.