ty in achieving revenue growth and managing prof- itability. Furthermore, subscriber acquisition costs have climbed dra- matically; according to industry reports, Sprint saw acquisition costs go from $285 in the third quarter of 2001 to $395 a year later, and later numbers bear out this continued increase. Like most segments of the industry, wireless faces further consolida- tion. As I write this section of the book, Sprint and Nextel confirmed this very morning their intent to merge, and others will undoubtedly follow in the wake of the collapsed telecom bubble. Today, six national operators serve 75 percent of the overall market. These players struggle to uniquely address the needs of a wider array of identified market seg- ments including high-volume business users, corporations with large numbers of users looking for deeply discounted pricing plans, extended families looking for deals, kids, and of course, new users. They are also looking for ways to satisfy the demands of prepay customers who are credit-challenged or have not yet established credit. Only recently, Virgin Mobile entered the U.S. market and is already making significant inroads. Virgin is a mobile virtual network operator (MVNO), which means that they own no infrastructure. They buy huge volumes of min- utes of use from other carriers at deep discounts and then resell them in prepaid mode, which means that they also have no billing infrastructure to support. The only organization they do support is-you guessed it, cus- tomer service. What a concept. Access Evolution Wireless access technologies have undergone an evolution comprising three generations. First generation systems, which originated in the late 1970s and continued to be developed and deployed throughout the 1980s, were analog and designed to support voice. They were characterized by the use of FDMA technology. In FDMA systems, users are assigned ana- log frequency pairs (and access to a control channel) over which they send and receive. One frequency serves as a voice transmit chann