Here in Aus, HSDPA will provide a max theoretical download speed of 7.2Mbps Phones like the SGS2, with HSDPA+ will support a theoretical max of 21Mbps. Both run on Telstra's "NextG" Frequency @850mhz, however makes no real difference as Telstra throttle their network to give a real download speed between 500Kbps and around 3Mbps. Phones like the SGS2, here in Australia will never really get to utilise their theoretical maximum speeds, as the Telco's will use bandwidth throttling to maintain network redundancy (and thus save money on investing in infrastructure upgrade works) Whilst it seems like our friends across the water like to market HSDPA+ as "4G", do the Telco's there actually support this with real maximum speeds on the Frequencies they run on? If not, HSDPA+ may not be of much use after all.
All's I know is: it serves up palmtop porn pretty promptly.