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If you’re still in the business of developing Windows Phone 7 apps, then this news is pretty important.

Microsoft is sending out emails to developers letting them know that after December 31, 2014, unlocking a Windows Phone 7.x device for testing purposes, like the Lumia 900, will not be possible. Unlocking your devices before the deadline will grant you additional 24 months of testing time.

If you’re still coding for Windows Phone 7.x, you should seriously consider migrating to Windows Phone 8.x as Microsoft ended the mainstream support for Windows Phone 7.8 a month ago.

You can upgrade your existing Windows Phone 7.x app to Windows Phone 8.x using both development stacks-Windows Phone Silverlight or WinRT. Here are some options with the respective pros and cons.

Upgrade to Windows Phone 8.0 Using the Windows Phone Silverlight Development Stack

+ Your app can run on both Windows Phone 8 and Windows Phone 8.1 devices.
+ You can use Telerik UI for Windows Phone 8 to speed your development process up.
- You cannot take advantage of the new features available in WinRT XAML.
- Your app cannot run on Windows 8.1 devices (large form factors).

Upgrade to Windows Phone Silverlight 8.1 Using the Windows Phone Silverlight Development Stack

- Users cannot run your app on Windows Phone 8 devices until they get the free Windows Phone 8.1 software update. Windows Phone Silverlight 8.1 apps run only on Windows Phone 8.1 devices.
+ You can use Telerik UI for Windows Phone 8 to speed your development process up.
+/-  You can take advantage of some the new features available in WinRT XAML. (See Supported features for Windows Phone Silverlight 8.1 apps.)
- Your app cannot run on Windows 8.1 devices (large form factors).

Upgrade to a Windows Runtime XAML App a.k.a. Universal Windows Apps Using the New Windows Runtime Development Stack

- You cannot use the Windows Phone Silverlight development stack. This means that you’ll have to rewrite your app.
+ You can take advantage of all the new amazing features that have been included in the new Windows Runtime. (See Migrating your Windows Phone 8 app to a Windows Runtime XAML app.)
+ You can support all devices (Windows Phone 8.1 and Windows 8.1) with the same code base (i.e. you will maintain one app instead of two or more).
+ You can take advantage of Telerik UI for Windows Universal to speed your development process up.

Sticking with Windows Phone Silverlight is the option that requires less effort. However, you should definitely consider investing the time to migrate to the new Windows Runtime as it offers much bigger development opportunities. Have you considered going cross-platform?

Take a look at the full text from Microsoft and let us know in the comments what your preferred approach is.

"Windows Phone Developer, 

Starting December 31, 2014, it will no longer be possible to unlock Windows Phone 7.x devices for app testing. We recommend that you unlock your Windows Phone 7.x devices prior to December 31, 2014 to continue testing with those devices for another 24 month. 

After December 31, 2014, no Windows Phone 7.x unlock capabilities will be available. This means, for those of you who have not unlocked your Windows Phone 7.x device, testing of apps directly from Visual Studio on that device will no longer be possible. However, app testing can still be done on other unlocked phones, or via the Windows Phone Emulator, or by submitting beta apps through the Windows Dev Center

Please note that this change will not impact apps available in the Windows Phone Store, nor will it impact customers with Windows Phone 7.x devices. Additionally, if you have apps that only have a Windows Phone 7.x package, now is a good time to update these apps to Windows Phone 8 or 8.1

Windows Store Team"

About the Author

Kiril Stanoev

Hi, I'm Kiril and I'm the Product Manager of Telerik UI for Android, Windows Universal and Windows Phone. Feel free to ping me on +KirilStanoev or @KirilStanoev

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