problem 3: phones don't connect to isp's they connect to carrier wap gateways.
One attempt to track mobile is from Opera but it's highly skewed to the type of people that have Opera on their phones and the activity that's significant for them: http://www.opera.com/mobile_report/
Old phones. iPhone, Android -- these are the phones of the future. In three years, most people will probably have WebKit or Gecko running on their phone.
The iPhone is already the best selling phone in the US.
So, for quantified sites, audience composition is extrapolated from ISP data based on what? The Quantcast provided explanation (http://www.quantcast.com/docs/display/info/Next+page4) is pretty light on concrete details of how it extrapolate demographic data from cookie info.
Would love to hear a straight forward answer for this one. My clients love the data available, but give it low validity because not clear how its derived.
-OR-
You insert some js in your pages, and it's "quantified". They actually have some pretty cool stats, and exact numbers unlike alexa.