I strongly belive HOs between 2G and 3G are needed. Why? Well, there any many reasons. Currently the coverage of the most 3G networks is not as good as with 2G, so if there were not HO from 3G to 2G, then user in the edge of 3G would experience drop if not handed over to 2G. This is just one example. Then, some vendors may have different type of algorithms to free 3G capacity for high bitrate users. This requires also HO from 3G to 2G in case where e.g. AMR call has been started in 3G, but it is wanted to be handed over to 2G. One more thing; building capacity even for AMR is much cheaper with 3G. One WCDMA cell can easily handle tens of calls, and for same amount of calls GSM cell would need quite big amount of TRXs. This will be trend we are seeing, and deployment UMTS900 will make 3G even favourable over the 2G.