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for some years now, cellular telephony systems have been experiencing a level of growth unprecedented in the world of telecommunications. When the first cellular technologies were brought into service, at the beginning of the 1990s, we saw a rather slow take-off in the curve of subscriber numbers, hardly presaging the subsequent spectacular growth. At the beginning of 2001, there were some 450 million GSM subscribers in the world (including more than 40 million in the UK) Figure 1.1). So-called second generation wireless technologies as a whole (GSM, IS-95, AMPS, PDC, PHS) serve a total of more than 600 million subscribers.