IMO for Windws Phone (7, 7.5, 7.8, 8, 8.1, 10) is not available yet as native app, but you can run IMO chrome app for your Windows Phone. If you are looking for Windows Desktop, then you are lucky becuase imo company launched IMO for Windows desktop versions recently.
Windows Phone (successor to Windows Mobile) is a smartphone OS developed by Microsoft and was made to be a strong competitor against iOS ( Apple ) and Android ( Google ). Windows Phone truly comes alive when the things you love are put in it. Photos, people, songs, places, and apps automatically update right on your Start screen. You can take your stuff virtually wherever you go with OneDrive, for sure, most secure than iCloud :). Since February 2011, Microsoft and Nokia announced a partnership between their companies in which Windows Phone would become the primary smartphone operating-system for Nokia, replacing Symbian.
Download imo for Windows (Desktop)
Download imo for Chrome (for Windows Phone)