Hello all iPhone lovers,just to share a bit of my experience how I prevent iPhone/iPod Touch from small tiny scratches that cause by small dust trap in cases.The method I'll share here will cost u small bucks but will give u the enough protection.Might not be good in out look but,well u can get branded Invisible Shield if you like.Just some sharing.TRY at your OWN risk.

1.For the Home Button
Home Button for iPhone 4 or anything similar are not made from glass,so they are actually quite vulnerable for hair line scratches , or worst big scratches.Most low-mid range Screen Protector do not offer small piece of cut out to protect your button,so what I do is

-Get a case that cover the Home Button example : switcheasy colors
-Get a box of Transparent Warping (those that apply to cover food)
-Clean Hands
-Cut a small piece of the transparent warping,fold 2~3 times and cover it on the Home Button
-After firmly attach it to the Home Button,slide it in the case.

The idea here is simple, sometimes trap dust will go inside the case and will cause the rubber to rub on the small dust then rub on the plastic surface of the button,from that it will cause tiny hairline scratch,it will be even more easy if it's left bare.So having a layer of transparent warping on top before direct contact with the home button will reduce the chance of small dust getting trap in between and cause scratches.

2.For iPhone 4 Stainless Steel Band
If you look through the web,there are topic circling that iPhone 4 original bumpers will case scratches to the stainless steel band.It is true that if dust trap between hard case,or very tight fitting silicon case it will give small dent,scratches on the stainless steel band.The stainless steel band is not as strong as it seems to be.

-Get a soft silicon case
-Get a box of Transparent Warping (those that apply to cover food)
-Clean Hands
-Cut a long piece and fold itself 2~3 times,then carefully warp around the stainless steel band
-Carefully fit the phone into the case,and be sure that it covers properly the steel band to prevent dust reaching it.

Finally,i found that transparent warping is good to prevent small dust,and can provide light protection to smaller areas of the phone like the front camera or the back camera.The following guide can be done with out getting a case,but it will look ugly.Hope it helps.^^