The hardware is already compatible. It just needs the software. A simple update for Windows Phone will make it work. Same thing goes for Android. And iOS. And Windows 8. And any other software that has wifi.
Most windows phones have WiFi direct with them which is what the xbox one controller uses. So it is possible for a developer to create something that recognizes the controller. We will probably see something hopefully by the end of the year. but don't take my word for it.