This is a quality shot. The composition is good, but there are a couple of issues I see. The skin shown is a small element of the photo. My attention is drawn to the face of the phone, which is well-lit, yet there is nothing noteworthy about it. The buttons look a bit muddy, that the may just be due to the 640 restrictions. There are pink and blue hues to the shadow and a hard line that seems out of place. Something that might have helped is a reflective surface to give the shot more depth. Of course, these are only my opinions. Take them with a grain of salt.
Don't get discouraged. This is a quality shot. All you have to do is look at the numbers of 1, 2, and 3 votes and you'll see that they were given because they didn't think it met the challenge. There are a lot of people voting who don't understand what a skin is...
Nice product shot.
This sort of skin was in my list of ideas.
Lighting and composition seem pretty good.
Maybe a bit of a colour cast, blue on the left.