Ben Lowe explains how to create your own WP7 icons even if you are not a graphic designer.
Source: Tribal Labs
I’m not one for purchasing icon packs as you often have to compromise on the appropriateness of the icon for the task at hand. Fortunately, due to the simplicity of the Metro style (warning PDF document) of the Windows Phone interface the icons are actually very easy to create yourself even if you aren’t a graphic designer. Also, to make life easier, you only need to create a single icon and the clever phone auto inverts it as required depending on the user’s theme settings and also adds the circle around the outside. You just need to create you icon (without circle) with a white foreground and transparent background.