@razefox
Your Skype contacts are where all other contacts are - in Contacts app. You can filter them by pressing top status bar and selecting appropriate filter.
You can call then the same way you are calling a mobile number.
And oh, you don't need no headset to call - just do it like you place a normal call, with the N900 next to your ear. That is the beauty of Maemo 5 - it integrates IM seamlessly and handles cellular and VOIP exactly the same way. This is one of a kind device in that aspect.