1 Introduction
Customer churn, switching from one service provider to another, destroys profits and decreases shareholder value. In the wireless telecommunications industry, the annual churn rate reaches 25% in Europe and 30% in the United States [1]. It costs around five times as much to sign on a new subscriber as to retain an existing one. In most developed markets, acquiring a new customer costs an average of $300 to $400. It is estimated that, in the mature markets of North America and Europe, churn costs wireless service providers a combined total of more than $4 billion each year [1]. It is thus crucial to predict customer behavior, e.g. churn, in advance. Accurate prediction may allow one to forestall churn by proactively building lasting relationships with customers.