From the Wikimedia Blog:
The data speaks for itself. Mobile page views rose over 75 percent in 2012, while desktop traffic grew at just under 20 percent. It is clear that much of Wikipedia’s growth is happening on mobile. We know that two things contribute significantly to this: 1) With mobile internet, readers have new reasons to look things up on Wikipedia, be it either related to context and location or convenience and availability, 2) Many readers in developing countries, specifically where there is limited broadband penetration, are using mobile devices as their first or only means to access the internet.
At the end of January, we reached another milestone: 3 billion mobile page views in one month. This means 14.5 percent of Wikipedia page views now are to the mobile site, up from 9.9 percent a year ago. Our target in the 2012-13 annual plan is to hit 4 billion monthly mobile page views by the end of the fiscal year (June 2013).
A look at the data accompanying past mobile milestones reinforces these reasons. In the 15 months it has taken for mobile traffic to triple (from 1 billion to 3 billion), overall Wikipedia traffic grew just 33 percent, indicating that many loyal readers are shifting their time to mobile devices. Secondly, when Wikipedia hit 500 million mobile page views two years ago, 71 percent of that traffic was to the English Wikipedia. Today, only 52 percent of mobile traffic is to English Wikipedia, illustrating that mobile growth has become a global phenomenon.
Read the Complete Wikimedia Blog Post
More on the management of Wikimedia mobile
Wikimedia CEO, Sue Gardner, Interviewed on Marketplace (Jan. 31, 2013)
Text Summary of Marketplace Interview