I have had Treos for the past 4-5 years and will occasionally drop my phone on concrete, carpet, wood floors,etc from 4 feet or so. However, the screen has never cracked. I know some people have cracked their Treo screen, but in my experience, maybe I'm lucky, but it seems to be crack resistant from drops. When I get my iPhone 3G, I want to go with Invisible Shields, BSE or something like that. However, after seeing several pictures of cracked iPhone screens, I am wondering if you need a case to protect it. How durable is the iPhone from the occasional drop?