i think the US figure is HSDPA and the UK one normal 3G The uk does have some HSDPA areas, but not many towns and cities support this.
Note to US people - there aren't that many towns and cities in the UK

(Note London's population is about twice the size of LA - but the U.S. has ~250 places with >100,000 population (and don't grumble about that not meaning a city - the UK is very historical about how things are or aren't a city (see Rochester, population of Wells etc))
O2 will likely be making a lot more of this map purple:
http://www.webmap.o2.co.uk/map.asp
There are 66 official cities in the UK
apparently
England:
Bath, Birmingham, Bradford, Brighton and Hove, Bristol, Cambridge, Canterbury, Carlisle, Chester, Chichester, Coventry, Derby, Durham, Ely, Exeter, Gloucester, Hereford, Kingston upon Hull, Lancaster, Leeds, Leicester, Lichfield, Lincoln, Liverpool, City of London, Manchester, Newcastle upon Tyne, Norwich, Nottingham, Oxford, Peterborough, Plymouth, Portsmouth, Preston,Ripon, Salford, Salisbury, Sheffield, Southampton, St Albans, Stoke-on-Trent, Sunderland, Truro, Wakefield, Wells, Westminster, Winchester, Wolverhampton, Worcester, York
Wales: Bangor, Cardiff, Newport, St David's, Swansea
Scotland: Aberdeen, Dundee, Edinburgh, Glasgow, Inverness, Stirling
About 1/8 of the population of UK lives in Greater London. I'd imagine that areas is covered pretty well! (roughly 8 million in Greater London, it's a fuzzy demarcation). That's in the region of 4,500 people per square kilometre (~1,800 per square mile) (mid-2006)
I'll exclude inner London.But the square mile will be HSDPA. To be honest, the Tube (opened 1863)is the place that most calls out for 3G / HSDPA.
The
"Key Statistics for Urban Areas 2001"[27] shows that the following are the largest 10 urban sub-areas outside London not a part of a city or having a city as a component:
* Reading – 232,662 (roughly the population of Jersey City NJ)
* Dudley – 194,919
* Northampton – 189,474
* Luton – 185,543
* Milton Keynes (urban area) – 184,506
* Walsall – 174,994
* Bournemouth – 167,527
* Southend-on-Sea – 160,257
* Swindon – 155,432
* Huddersfield – 146,234
Can you name 10 cities or urban sub-areas not on the HSDPA map ?

We already know that 3G covers >80% of the UK population. (Ofcom helped there)