, who are often also the manufacturers of cellular base stations and network equipment. On an engineering level, existing GSM systems are well established and cannot share spectrum with CDMA systems because the CDMA will interfere with TDMA broadcasts. This leaves only three options: new spectrum allocations, spectrum con- version channel by channel, or total conversion of a whole network all in one day. The first option requires government allocation of spectrum, which usually takes a number of years. The second is an engineering challenge, especially since wideband CDMA (W-CDMA) has no guard bands. If a GSM channel borders on a W-CDMA channel, it will be difficult to ensure that there is no significant interference. To the best of our knowledge, such a solution has not been developed and tested. Channel-by-channel conversion is difficult for capacity planners, who must gauge the demand for two types of frequency, predict the change in that demand in each sector or region, and be pre- pared to switch frequencies over quickly so that neither the old system nor the new one is overloaded. The third solution is not feasible unless dual-mode telephones are made available to every cell phone owner in Europe. International interoperability across the continent and to many other places across the world is a key feature of GSM. Multi- frequency GSM telephones are common, allowing international travelers to use their own phones in other nations with services on different frequencies. A multimode cellu- lar telephone, though, is much more expensive because it has to include both TDMA and CDMA transceivers. Meanwhile, the effort to deploy systems that meet the W-CDMA standard has encountered a number of technical barriers, as discussed in Sec. 9.2. What will happen in the long run remains to be seen. CDMA has significant capac- ity advantages over TDMA, but a huge existing network does not change quickly. Coax- ial and fiber-optic cable have tremendous capacity advantages over copper twisted pair for landline services. Howe