Take this with a heaping cup of salt, but Tweakers.net is reporting from multiple sources that Sony is planning on joining the Windows Phone camp late in 2012.
Of course there are hurdles in the way such as Sony and that whole Playstation thing, but Sony is like any other massive corporation and its departments operate independently of each other, so we wouldn't actually cite that as a reason not to. Heck, we know that back in 2010 Sony-Ericcson seemed just fine with the whole notion even going so far as to make a few prototypes for early development. Obviously if SE had no problem with the Xbox system we don't see why Sony (sans Ericsson) would either.
Still, there's no hard evidence here for this just past experience so we'll just have to keep an ear out. Should Sony though decide to make some Windows Phones, especially with waiting for WP8 that could be a very good thing for customers.