 number of choices of products and suppliers when new generations of services are developed to handle additional video and data. In addition, carriers are faced with the challenges of managing many different generations of technologies including second-generation (2G), third-generation (3G), advanced 3G, and pre-4G services. Although Software-Defined Radios (SDRs) have made it less complex to upgrade cell sites, managing multiple bands of spectrum along with multigeneration services requires complex diagnostics and staff members with the ability to support older 2G gear as well as newer, more advanced, pre-4G equip- ment and software in both the core and cell sites. In addition to managing complex networks on a day-to-day basis, carriers need to create strategies for upgrades and maintenance that are affordable and enable them to keep prices competitive. For these reasons, carriers are signing contracts to outsource maintenance of all or part of their infrastructure to manufacturers. Part of the rationale for outsourcing is the desire to save money on maintenance staffs and to concentrate corporate resources on competitive strategic initiatives, such as marketing campaigns Appendix or development of competitive offerings. For all of these reasons, carriers are also starting to share network infrastructure with other carriers. One strategy for both attracting customers and earning revenue is to host applica- tions that subscribers can download to mobile devices. Developers use specialized software to create these applications, which on mobile device are typically called apps. In return for making apps available to subscribers, developers share the revenue they earn with carriers. The general rule of thumb is that carriers receive 30 percent of the fees that subscribers pay and the rest goes to the developers. The downside for subscribers is that many apps are not portable. Thus, subscribers who change carriers might lose all of their apps. APPENDIX Table 7-3 Mobile Services Worldwide Technology Frequencies Feature