Microsoft has rolled out Skype for Windows Phone which is now in final state, as previously in February 2012, Skype beta for Windows Phone was released at Mobile World Congress.
Skype for Windows Phone allows users to make calls free of charge over 3G, 4G or Wi-Fi networks. The latest Skype for Windows Phone supports 18 languages and works with Windows Phone 7.5 Mango or later devices.
Download Skype for Windows Phone
See also:
Download Skype for Android
Download Skype for iOS