In this post Michael Wolf shows how to utilize the Skype4Com api with Silverlight 4.
However the biggest improvement here is the inclusion of elevated privileges, which allows you to get access to the local file systems at a pretty broad level, but more importantly access to locally registered com objects. This means direct access to integrate with things like word or excel, like you will see in most demos, but also the huge community of com objects like skype. When I first saw this feature, I remembered that back in the bad old silverlight 1.1 days I investigated using Skype to make phone calls via the java script bridge. What I found was that skype makes available a very rich com api known as SKype4Com.