A user from a Hong Kong-based message board posted pictures of his iPhone 4 mod, which replaces the front and back covers with transparent versions. This exposes components typically not seen, such as the battery and lots of screws. No important parts like the processor and memory chip are visible, though, as those are hidden inside.
According to the owner, the original replacement parts were not transparent--he scraped the paint off to achieve the effect. Those who thought they were going "naked" by simply not using a protective case could perhaps go a step further with this mod.