The main advantages the 900MHz band has over 2100MHz for 3G is...[LIST][*]Better in-building penetration - should be most noticeable in built-up areas (where outdoors 2100MHz 3G may be fine but struggles indoors especially at ground floor level) but everywhere can benefit from this.[*]Better coverage from a single mast - main benefit here is for rural coverage where 2100MHz 3G is deemed uneconomical - approx. four 2100MHz base stations are needed to match the coverage area of 900MHz 2G in rural areas on average. In addition, UMTS does not have a 35km radius limit that GSM has so in very desolate areas its possible to mount that base station on a mountain mast to cover a very wide area not dissimilar to a medium-powered TV transmitter (200km has been proven from aircraft, real world ground level results are likely to be less than half of this). For urban areas, 900Mhz would likely be better suited to microcells and picocells rather than macrocells.[*]For the same transmitting aerial above ground level at the same centre frequency with the same output power, the 5MHz UMTS block will give better coverage than the 200kHz GSM allocation (in the absence of on-channel interference) as UMTS can work down to lower signal levels approx 10db better than GSM in good conditions, though UMTS' coverage can be affected by cell breathing particularly during peak times.[/LIST]There is a price to pay for 3G deployment in the 900MHz band however, and that is reduced spectrum available for 2G (GSM) services. This can be partially offset at least by adding 1800MHz spectrum at the same site (both O2 and Vodafone have small allocations) if spectrum is available to deploy. Adopting Half-Rate speech coding is also an option for 2G calls, though this results in lower call quality.