The Windows Phone 8 supports 3 different screen resolutions like WVGA,WXGA,720P .
If you are a developer and want to retrieve the screen resolution dynamically , you can use the ScaleFactor property defined in App.Current.Host.Content.ScaleFactor.
string data = App.Current.Host.Content.ScaleFactor.ToString();
This will retrieve the one of the 3 values 100 , 160 , 150 which refers to the screen resolutions (WVGA , WXGA and 720P) respectively.
From this Forum thread:
Screen Resolution for Emulator