Added support for WP8 and WP8.1. Tested in WP8.1 emulator.

plugin.xml

@@ -52,4 +52,16 @@
         </js-module>
     </platform>
 
+  <platform name="wp8">
+    <config-file target="config.xml" parent="/*">
+      <feature name="YoikScreenOrientation">
+        <param name="wp-package" value="YoikScreenOrientation"/>
+      </feature>
+    </config-file>
+	  <js-module src="www/screenorientation.wp8.js" name="screenorientation.wp8">
+		  <merges target="cordova.plugins.screenorientation" />
+	  </js-module>
+    <source-file src="src/wp/YoikScreenOrientation.cs" />
+  </platform>
+
 </plugin>

src/wp/YoikScreenOrientation.cs

@@ -0,0 +1,127 @@
+/*  
+	Licensed under the Apache License, Version 2.0 (the "License");
+	you may not use this file except in compliance with the License.
+	You may obtain a copy of the License at
+	
+	http://www.apache.org/licenses/LICENSE-2.0
+	
+	Unless required by applicable law or agreed to in writing, software
+	distributed under the License is distributed on an "AS IS" BASIS,
+	WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+	See the License for the specific language governing permissions and
+	limitations under the License.
+*/
+
+using System;
+using System.Net;
+using System.IO;
+using Microsoft.Phone.Controls;
+using Microsoft.Phone.Notification;
+using Microsoft.Phone.Shell;
+using System.Windows;
+using System.Windows.Controls;
+using System.Windows.Documents;
+using System.Windows.Ink;
+using System.Windows.Input;
+using System.Windows.Media;
+using System.Windows.Media.Animation;
+using System.Windows.Shapes;
+using System.Windows.Threading;
+using System.Runtime.Serialization;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.Globalization;
+using System.Threading;
+
+using WPCordovaClassLib.Cordova;
+using WPCordovaClassLib.Cordova.Commands;
+using WPCordovaClassLib.Cordova.JSON;
+
+
+namespace WPCordovaClassLib.Cordova.Commands
+{
+    public class YoikScreenOrientation : BaseCommand
+    {
+        #region Static members
+
+        private const string UNLOCKED = "unlocked";
+        private const string PORTRAIT = "portrait";
+        private const string LANDSCAPE = "landscape";
+
+        #endregion
+
+        /// <summary>
+        /// Current orientation
+        /// </summary>
+        private string currentOrientation;
+
+        public YoikScreenOrientation()
+        {
+
+        }
+
+        /// <summary>
+        /// Changes the orientation
+        /// </summary>
+
+        public void screenOrientation(string options)
+        {
+            string orientation = null;
+            try
+            {
+                orientation = JSON.JsonHelper.Deserialize<string[]>(options)[0];
+            }
+            catch (Exception ex)
+            {
+                this.DispatchCommandResult(new PluginResult(PluginResult.Status.JSON_EXCEPTION, ex.Message));
+                return;
+            }
+
+            if (string.IsNullOrEmpty(orientation))
+            {
+                this.DispatchCommandResult(new PluginResult(PluginResult.Status.JSON_EXCEPTION));
+                return;
+            }
+
+            if (this.currentOrientation != orientation) // Might prevent flickering
+            {
+
+                Deployment.Current.Dispatcher.BeginInvoke(() =>
+                {
+                    PhoneApplicationFrame frame;
+                    PhoneApplicationPage page;
+                    if (TryCast(Application.Current.RootVisual, out frame) &&
+                      TryCast(frame.Content, out page))
+                    {
+                        if (orientation == PORTRAIT)
+                        {
+                            page.SupportedOrientations = SupportedPageOrientation.Portrait;
+                        }
+                        else if (orientation == LANDSCAPE)
+                        {
+                            page.SupportedOrientations = SupportedPageOrientation.Landscape;
+                        }
+                        else if (orientation == UNLOCKED)
+                        {
+                            page.SupportedOrientations = SupportedPageOrientation.PortraitOrLandscape;
+                        }
+                        else
+                        {
+                            this.DispatchCommandResult(new PluginResult(PluginResult.Status.ERROR, "Screen orientation not detected."));
+                            return;
+                        }
+                        this.currentOrientation = orientation;
+                    }
+                });
+
+                this.DispatchCommandResult();
+            }
+        }
+
+        static bool TryCast<T>(object obj, out T result) where T : class
+        {
+            result = obj as T;
+            return result != null;
+        }
+    }
+}

www/screenorientation.wp8.js

@@ -0,0 +1,8 @@
+var exec = require('cordova/exec'),
+	screenOrientation = {};
+
+screenOrientation.setOrientation = function(orientation) {
+	exec(null, null, "YoikScreenOrientation", "screenOrientation", [orientation]);
+};
+
+module.exports = screenOrientation;