I do this once in a while. I have a Google Voice number, and a Skype subscription. I have Google voice set to ring both my iPhone number and Skype on my Mac. If I receive a call on my iPhone, and then realize that I would prefer to take the call on Skype on my Mac, I press the * key on my iPhone, Skype on my Mac rings, and I take the call through Skype on my Mac. It works very well, and is very simple, once you get a Google Voice number and a Skype subscription.