When I saw Apartment Therapy's Home geek tip that I didn't know existed, I had to try it out. While on vacation, they forgot iPhone speakers, and therefore improvised by putting their iPhone in a cabinet, which acted as a makeshift speaker.
They say "the wood warmed it up and gave it a little more resonance than it would normally have." Since I use my iPhone for music at home when I need the portability (in the kitchen, etc.), without any sort of help, I wanted to try out AT's tip.
To find out what happened when I tried the wooden cabinet tip, just
I tried a mounted wooden cabinet, then my wooden medicine cabinet. For me, all I got was a muffled version of my iPhone speakers. I even tried putting it, sound blaring, inside wooden drawers. Nope. The iPhone sounded better without any assistance, but of course, not as great as it would with external speakers I'd plug it into. In or out of the cabinet is sort of a last resort anyway, but maybe you could try this trick out at home and see if it works for you.