Ive never put a case or protection on any of my phones. Ive dropped my Incredible many times, not even a slight crack. The worst thats happened to it are some scratches on the corners.
I managed to drop a Galaxy S3 onto an asphalt parking lot when i was trying to put it into the inside breast pocket on a sports coat and missed the pocket.
I had a very basic plastic case on it.
The phone hit on a tiny exposed bit of one corner and the screen broke with cracks going top to bottom. The Galaxy S3 is solid glass from top to bottom, and perhaps more prone to breaks than other phones. A local place could replace the glass, but the glass and the LCD screen are bonded together, so the part is about $235.
I very seldom drop a phone, and had never damaged one before by dropping it.
I got another identical phone - it's a university phone and we had upgrade eligibility, so i just burned one upgrade for my unit to get a replacement phone.