Hi Paolo,
What you're asking for (accurate, current and detailed user and hardware stats) is a bit like the holy grail of the mobile world. Very hard to come by, although you will find plenty of places claiming certain numbers as fact, when they are either hopelessly out of date or plain wrong.
If it's subscriber numbers you need, GSM World is good, but AFAIK those numbers don't take into account multi-SIM users or phone-sharing (very common in the developing world) for example. Obviously you don't get any help on phone type, OS etc either.
Screen resolution and general hardware stats are more difficult, because it's even harder to track how many phones people have and if they use them. So sales numbers are not that useful if you want to build a mobile service of any kind. If you look at, say, Nokia's sales releases, they just shout "we've sold x million devices" but that doesn't tell you what people do with them, or who these people are demographically.
Some good technical device stats are released now and then by
m:metrics (who sell them)
admob release a monthly list generated by their ad tracking on mobile web sites. That gives you the 20 or so most popular handsets among mobile web users - you then need to find out the technical details of those if you want the JVM/Screen resolution etc. But those details are easily found on the manufacturers' sites. Admob are also planning to release a
free analytics service soon, which should be handy.
It's interesting to see how these lists change according to the target audience. When you looked at the games and application aggregator Bango's monthly
device download chart (sadly not maintained since Nov 2007) you used to get very different handsets to the more business-oriented stats providers. But other demographic data you could only get by looking at download stats of relevant sites or by getting detailed subscribers data from the mobile networks - which they won't give you.

There are probably many more places to look, but as always it's tricky to get 'good' statistics...
Wolf.