China now is a little like Japan in 2000 or so - it's where a lot of the most important and interesting things in mobile and tech are happening, and it's also something of an information black hole if you don't speak (or more accurately read) the language or have an office there.
There is some basic resource readily available, though. Most obviously, the CNNIC, a quasi-governmental organisation, produces a twice-yearly statistics report: the 32nd issue was just released. So far it's only out in Chinese - an English version will follow. These two charts show first internet users and then mobile internet users, both in 10ks.
So, 590m internet users and 436m mobile internet users. This latter number, interestingly, is a fair way ahead of 3G users, as provided by the mobile operators, which stood at 280m at the end of March. Lots of wifi in that use.
There's lots of other interesting data, but this chart really stands out. It shows the means by which people access the internet. The first group is desktop computers, the second laptops and the third mobile phones.
The implication of this chart is that a little over 30% of Chinese internet users only have mobile access, and close to 80% use mobile at some point.
The proportion of these mobile users that have smartphones is a little less clear, at least if you prefer to rely on primary sources. Baidu reported that 46% of its mobile page views came from iOS or Android in Q3 2012, up from 16% at the beginning of the year; one would expect these devices to have disproportionately high page views, but by now it seems clear that they've passed 50% of the base. That would imply well over 200m now - perhaps three quarters of that is Android. There are more solid estimates out there - I'm still gathering data to make my own.
These are (obviously) big numbers. To put this in context, there are only a little over 300m total mobile users in the USA, of which around 150-160m have smartphones, depending on which survey data you use. China already has significantly more smartphone users than the USA. Unlike the USA it's dominated by Android, but of course most of those Android devices have no connection to Google.
This is why Baidu bought 91 Wireless, which runs two of the biggest Chinese Android app stores. With limited access to Google Play (and no Play payments), there are dozens of alternatives. In fact, there are also alternatives to Apple's app store - partly for piracy and partly because until recently downloads across the Great Firewall were very slow. These stores only work on jailbroken iPhones, but around a third of Chinese iPhones have been jailbroken. Overall, Baidu claims 91's stores have had over 10bn app downloads (probably including iOS) - for comparison, Google Play downloads recently passed 48bn.
It's also worth tracking companies like Wandoujia. It's another of the dozens of stand-alone Android app stores, and it's started doing a stats deck to boost awareness amongst foreign developers. It claims 120m mobile users, of which 12m open the app store app every day, and 26m app downloads a day.