Check your math: "Let's say they have 1 million active paying customers (nonsense, but what the Hell), each of those would have to be valued $100 to make Skype worth a billion. That is about twice the going value of a mobile phone customer. Ridiculous." You are off by a factor of 10. If there are 1M customers, each is worth $1000 - about 20 times that of a cell phone customer.