In the coming 12-18 months, cellular operators in many Asian countries will have to decide which technology to adopt as they undertake the costly migration of customers from analogue to digital mobile systems. Considerations include cost effectiveness, roaming compatibility and how these services will become compatible with 'third generation' high-speed data networks. There is little doubt that Asia has taken the European GSM digital system to heart, but this operates at 900MHz, 1800MHz and 1900MHz frequency ranges in the many countries (including Hong Hong and the mainland) GSM technology dominates. However for those countries or operators which have operated AMPS analogue technology at 800MHz, and there are many of them, the choice of moving to GSM does not exist. Markets falling into this category include Indonesia, Thailand and the Philippines. All have AMPS networks and are due to make decisions on what digital technology they intend to adopt. 'In Asia there is a big AMPS base,' said Urban Gillstrom, of Swedish equipment-maker Ericsson. Practically speaking, this leaves two choices - D-amps , also known as the IS-136 standard, and CDMA (code division multiple access), known as IS-95 standard. These two, although both US standards, use different technology promoted by differing vendors. As they move to digital a battle is looming for Asia's 800MHz operators. A key move came this week that appears to have strengthened the hand of those promoting D-amps. It uses the same method of signal transport as GSM, both utilising time division multiple access (TDMA) technology, putting them much closer together than CDMA. In the past, roaming between GSM and D-amps has not been possible. However, under a new framework agreement the industry bodies representing the D-amps, Amps and GSM systems have laid the foundations for a worldwide agreement to produce roaming pacts. Roaming between the standards will continue to require a dual-band or tri-band phone, but in future it should be possible to use one SIM card for all networks. These 'world' phones should be on the market later this year. For Asian mobile-phone users, especially those using GSM, the main world 'black hole' has been the United States, which has used a mish-mash of technologies but itself increasingly is moving towards nationwide coverage using D-amps. AT&T, the USA's largest cellular provider with about nine million subscribers, has chosen D-amps as it is nationwide platform of choice. A convergence of D-amps and GSM will be a powerful incentive for operators to look at D-amps as their next technology. The two are the world's dominant standards with more than 225 million subscribers. Where does this leave CDMA? Well, not completely out of it. Proponents still believe it is better for clarity and cost effectiveness, with more voice channels per base station than TDMA. This is important for developing countries which are focused on improving basic service penetration rather than trying to serve a small band of roaming customers. However, Ericsson's director of D-amps business in the US Vu Nguyen said the nature of the CDMA 'soft hand off' system meant that entire networks had to be built out, no matter how many users it had from the beginning, whereas TDMA could be built incrementally to suit growth in users. He said the cost of building a TDMA network was about US$8 per subscriber, while CDMA was about $10 per user. Ericsson does not make CDMA equipment and the battles between CDMA firms the likes of Ericsson are well-documented, and sometimes bitter. However, whatever the claims on clarity or cost, TDMA has stolen a huge advantage in terms of its roaming potential. TDMA also holds another ace. Because GSM and D-amps use similar time-division technology, their paths to higher data rates of the future are much closer. In fact, as the data-speed over the network improves the technologies will merge. What does this mean? Take Hongkong Telecom. It operates both a GSM network and a D-amps network, known 1+1. When the new technology is introduced that allows more capacity of information to go over the airwaves quicker, the two systems could function as one for delivering data services. This is still some time off, but the attraction in terms of cost savings for providing these higher speed data services is another factor to be considered. Hutchison, which has GSM and CDMA networks, will not be able to gain from the same efficiencies at those higher data rates. The networks will take different technology development paths, a more expensive exercise. One interesting aside is the mainland. It is dominated by GSM networks using both 900MHz and 1800MHz technology to provide huge capacity. In addition, the People's Liberation Army (PLA) has nationwide spectrum at 800MHz which it was going to use for CDMA, in a joint venture between the PLA and the Ministry of Information Industry which runs all other networks. However, after four trial networks were built in 1997-98, no national go-ahead was given for CDMA roll out. With the PLA ordered out of commercial activities and D-amps appearing to have so much better roaming capabilities, perhaps it is in a better position to be the technology of choice for the mainland's 800MHz spectrum. Because the country is so big, national roaming is an important issue. 'We believe there is a future for D-amps in China,' Mr Gillstrom said.