It took a fair bit of research, but in the end it was pretty easy. Hopefully this serves as a reasonable example of how to interact with Android's Java environment from within Unity.

using UnityEngine;

public class DisplayMetricsAndroid {

    // The logical density of the display
    public static float Density { get; protected set; }

    // The screen density expressed as dots-per-inch
    public static int DensityDPI { get; protected set; }

    // The absolute height of the display in pixels
    public static int HeightPixels { get; protected set; }

    // The absolute width of the display in pixels
    public static int WidthPixels { get; protected set; }

    // A scaling factor for fonts displayed on the display
    public static float ScaledDensity { get; protected set; }

    // The exact physical pixels per inch of the screen in the X dimension
    public static float XDPI { get; protected set; }

    // The exact physical pixels per inch of the screen in the Y dimension
    public static float YDPI { get; protected set; }

    static DisplayMetricsAndroid() {
       // Early out if we're not on an Android device
       if (Application.platform != RuntimePlatform.Android) {
         return;
       }

       // The following is equivalent to this Java code:
       //
       // metricsInstance = new DisplayMetrics();
       // UnityPlayer.currentActivity.getWindowManager().getDefaultDisplay().getMetrics(metricsInstance);
       //
       // ... which is pretty much equivalent to the code on this page:
       // http://developer.android.com/reference/android/util/DisplayMetrics.html

       using (
         AndroidJavaClass unityPlayerClass = new AndroidJavaClass("com.unity3d.player.UnityPlayer"),
         metricsClass = new AndroidJavaClass("android.util.DisplayMetrics")
       ) {
         using (
          AndroidJavaObject metricsInstance = new AndroidJavaObject("android.util.DisplayMetrics"),
          activityInstance = unityPlayerClass.GetStatic<AndroidJavaObject>("currentActivity"),
          windowManagerInstance = activityInstance.Call<AndroidJavaObject>("getWindowManager"),
          displayInstance = windowManagerInstance.Call<AndroidJavaObject>("getDefaultDisplay")
         ) {
          displayInstance.Call("getMetrics", metricsInstance);
          Density = metricsInstance.Get<float>("density");
          DensityDPI = metricsInstance.Get<int>("densityDpi");
          HeightPixels = metricsInstance.Get<int>("heightPixels");
          WidthPixels = metricsInstance.Get<int>("widthPixels");
          ScaledDensity = metricsInstance.Get<float>("scaledDensity");
          XDPI = metricsInstance.Get<float>("xdpi");
          YDPI = metricsInstance.Get<float>("ydpi");
         }
       }
    }
}

var widthInInches = Screen.width / Screen.dpi;

To add to Daniel's answer, for those who do not know how to implement this script you can simply add it to the Plugins folder (in your project hierarchy, you can add one if you don't have one) and call any of DisplayMetricsAndroid() variables, for example:

Debug.Log(DisplayMetricsAndroid.WidthPixels);

ofcourse, it has to be used within an Android enviroment. Thanks again Daniel.

Help, apply this in te GUITexture?

really great, thanks a lot