i give him an "A" for effort, but i am going to give a critique.
The Skype logo is too large. it should be smaller.
The iPhone doesn't use the same drop down menu graphics as normal OS X so he should probably find a picture of that or create it himself.
The Glossy buttons at the bottom need a little more contrast between the words and the color. Maybe just back down the gloss effect a little.
I myself am working on what i call "iPhotoshop" mockup for the iPhone. Just something that started out as fun, and has really become a challenge to think out.
Looks good though
-JE