My Windows Mobile phone broke a few months ago and Sprint wouldn't honor my insurance (but that's another story), so I can't personally test Facebook for WinMo. (I'm now waiting for the Pre to come out in early June.)

The social networking site has come to the Windows Mobile platform after successful launches on BlackBerry and the iPhone. It's not on Android however. But given Microsoft's investment in Facebook and the ads and search partnership the two have, it's a bit curious it took this long. Here are some screenshots of the Windows Mobile interface, which is quite different than the look and feel of the iPhone app. 

I would also expect that at some point the search partnership between the two companies will come into play in mobile. Right now on Facebook's mobile sites all you can do is search contacts.

Facebook has emerged as one of the top mobile sites in the US and Europe according to Opera. And Facebook reportedly sees more than 25 million monthly uniques accessing the site from mobile devices on a global basis. Despite these numbers, still only a small percentage of social network users access their networks on their handsets. Our latest US survey numbers indicate that there's been a doubling of mobile social networking (accessing social networks from mobile devices) since last year -- but from a small base. 

Here's more discussion of the app from Techmeme.