Freebbble!

From the author: “720×1280 display area, vector shape based. Feel free to use it anywhere you want, but please do not redistribute.”

Galaxy SIII White & Black PSD Template is a free Mockup design resource made by Dribbble user Eryk Pastwa. As far as I can tell, its license is Free for Commercial and Personal Purposes.

Helpful hint: Dribbble users are nice. If the license is unknown, it is usually because they forgot to mention it explicitly; not because they were being stingy. Ask nicely and they will probably allow you to use it.