 retail price of Mbit/s versus time. (After Fiber Field, D., Fire the Phone Company: A Handy Guide to Voice Over IP, Peachpit Press, Berbeley, CA, s.l., 2005, ISBN-13: 978-0321384867.) In front of this technical effort, the average price for unit bandwidth decreases continu- ously, SO that the increase in offered bandwidth generates almost no revenue increase. The price reduction is shown in Figure 2.8, where the U.S. average price of 1 Mbit/s in the access line is shown versus the time in a 2 year period. Even in SO short a time, the decrease in the price is evident, and the trend has lasted since the early 1990s. The fast price decrease generated by the Internet revolution also hit the standard telephone. Even in the Internet era, telephone is by far the telecommunication service that attracts more customers. Thus, the commercial war among carriers also brought about a relevant decrease in telephone prices. This decrease was also caused by the emergence of IP and mobile phone services. On one side, free IP phone, although not SO diffused, constitutes a dangerous competitor for standard telephone, especially for international calls, where the tariff of the main carriers is higher [28,29]. As far as the mobile phone is concerned, as underlined in the previous section, it has the advantage of being a personal communication device. Since the start of the massive diffusion of GSM phones, several people have replaced their fixed-line phones with mobile phones [30]. Under the combined pressure of internal competition among carriers and external com- petition from service providers using other technologies, telephone prices have been con- sistently going down since the early 1990s. As an example, in Figure 2.9, the average price of a phone call in different European countries is shown versus time in the period 1996-2004. All the prices are averaged on real traffic and reported as percentage of the average price in 1996. The price fall is quite evi- dent, and even if its importance is higher in the bubble years and beco