If you are an external developer engaged in Skype based application, then grab official Skype app icons for consistent user experience and Skype interface familiarity to the users.
There are over 100 icons in 5 different image sizes (16×16, 24×24, 32×32, 48×48, 128×128). Icons are in PNG image format and are licensed to all developers under the Skype Component License.
You can use these icons for free in your Skype-related products as long as you follow some simple restrictions (like use the icons in the same way they are used in Skype software, your product does not do anything evil, and a few others).