I love your project! Not only clean and simple, the use of Skype is brilliant! Just like Newtons apple, its easy to understand but tricky to invent.
Could you describe, in just a few words, how you handle the Skype in the Arduino end? Answering only the right call and transferring the order to a serial? I will read the source later.
Does Skype need a server connection or is it true peer to peer? Is it possible to use it in a closed network, without an internet connection?
Btw, that comment of Davide (the Global Moderator!) must be a killer!