From Wikipedia: O2 launched their HSDPA services across the UK in the third/fourth quarters of 2007 following an extended trial period, during which compatible devices were introduced. Coverage extends to most of O2's 3G footprint. Initial download speeds are 1.8 Mbit/s (peak), increasing to 3.6 Mbit/s (along with HSUPA) in June 2008. Not that we needed any more confirmation of a 3G iPhone. This does at least suggest immediate or close availability of the 3G model.