NokiaWP received images of a Sony(still Ericsson) phone running on Windows Phone 7.5. Earlier in 2011, SonyEricsson said that they will not use WP as a platform when they chose Android over WP as their only platform. But who knows things might have changed after Sony took over SonyEricsson.
What does this all mean? Unfortunately, we don't have any evidence that SE (or just Sony going forward very soon) has any plans for a Windows Phone. But Mobile World Congress is coming up at the end of February, so who knows maybe Sony will have something to present.
Via NokiaWP