i've decided to sell one of my 8gb iphones and to wait for the new iphones to come out... but the problem is that i've got this damn wallpaper on it that doesnt go away, not even when i try to replace it with another one. is there any way that i can completely erase an iphone so that none of my crap is installed on it? in other words, make it like it was when i took it out of the box for the first time?