Radio transmissions have opened new frontiers allowing the exchange of information with remote units. From the first applications of telegraphy and radio broadcast, wireless transmissions have obtained a great success with the widespread diffusion of mobile communications. We live in the communication era, where any kind of information must be easy accessible to any user at any time. Mobile communication systems are the technical support that allows the realization of such concepts. With the term mobile communications we embrace a set of technologies for radio transmissions, network prools, mobile terminals and network elements. The widespread diffusion of wireless communications is making national borders irrelevant in the design, delivery and billing of services, thus requiring international coordination of standardization efforts in order to evolve regional systems towards global ones. Parallel to the evolution of radio-mobile systems, we assist to the massive diffusion of Internet network and contents, thus allowing many users on the earth to be interconnected and to exchange any kind of information, data, images and so on.