sitive. The shift from second- generation (2G) to third-generation (3G) CMDA technology and the use of more effi- cient CDMA engineering techniques will allow vendors to compete for existing CDMA customers by offering the more efficient 3G air interface at lower cost and higher quality. In a few years, the wireless market will be almost entirely 3G CDMA, and the source of subscribers for one company will be competing for the subscriber base of another company. The fourth source of wireless subscribers is our own service's current subscriber base. In making a market estimation, this is our starting point, but we cannot assume that it is static. We may be losing or gaining customers due to churn. Estimating future churn is part of our estimation planning for the demand for voice service. This tells us that the long-term estimate of wireless voice call demand for any given provider depends primarily on the estimate of wireless voice market share. As the mar- ket size stabilizes, a service provider's share of the market becomes the primary deter- minant of the subscriber base. It is important for a CDMA vendor to form a clear idea of its position in the CDMA voice market in each region it serves. While studies of market share are a critical function, it is important not to lose sight of the ultimate objective of voice market estimation-figuring out the total demand for telephone service and how much of that demand will be carried on wireless networks. The investment in cells, transport, switches, and other equipment is an amount of money that depends on the absolute number of subscribers. Another important variable in the initial demand estimate is the planning horizon for the initial system. Planners have to decide how far into the future growth of the sys- tem they are planning for in the initial system design. By building in enough capacity to handle a period of initial growth after startup, we give ourselves time to get things running smoothly before we have to deal with growth issues. Getting a system up and run