Why not try a case like this?:
http://www.amazon.com/Options-Mivizu-genuine-leather-Generation/dp/B004E83Q9Q/re f=pdsim_sbs_e2
I've got one very similar, and it protects the front and back of the iPhone perfectly. I've got no scratches at all after 2+ months. I also had a leather flip-style case for my iPod Touch, and after about 2 years, it has not one scratch. A lot of these flip cases are really nice because they really don't add any bulk to the phone at all, and you can still slip it in your pocket, or purse, or whatever.
What I do like to do is make sure that I keep dust and stuff off the phone whenever I can, with a gentle sweep of the side of a finger. I know that even dust can scratch when it's rubbed against glass in the right -- or WRONG! -- way. 🙂
The way I look at it, the phone is worth over $700 (mine is), what's another $50 bucks or so to get a good quality case to protect it? This is the case that I have my iPhone in: (it doesn't have the cutout for the Apple logo on the back as pictured - which I prefer):
http://www.amazon.com/iPhone-Novoskins-iStyle-Flip-Green/dp/B0042QVC3W/ref=sr12?ie=UTF8&qid=1298361677&sr=8-2