It took the iPhone 3 years to hit 30% enterprise support. It seems 6 months after release Windows Phone 7 can at least say they are accepted into 31% of enterprise settings, if not fully supported.
Fully supported numbers are much lower, at 13%, around the same as Symbian, and will likely depend on Microsoft building more tools into their own enterprise solutions and of course into Windows phone 7.
While Microsoft has announced many new enterprise features for Mango, many of those do not slot neatly into the tools like their own Microsoft System Centre Mobile Device Manager and full device encryption, which allows features like remote application deployment which is essential for full enterprise support.
Fortunately enterprise device heterogeneity is increasing, with most businesses supporting on average 2.9 Operating Systems, but clearly the route to increased adoption is standards support, not unique solutions.