Trailmap is a real 3D offline map software for Windows Phone. It is unique, because this program is the only one for this platform, what can use Garmin’s IMG map file. Many communities offer IMG file export, like OpenMaps or garmin.openstreetmaps.nl. Another unique feature is a 3D altitude map. Simply upload the HGT file like a map, than you can see the hills, valleys.
Because the application is support Windows Phone 7, you have to use Trailmap Manager open source application, to upload maps. But the good side of this, you can choose which type of map you want to use.
The application is available in trial mode, in this version the application is not using your GPS position. But you can check your favorite maps. The full version is cost 4.49 USD.