Microsoft recently released the Windows 10 Technical Preview for Phones, but it's only available for six smartphones, none of which are high-end. As expected, this didn't go down well with anyone, and the online community started looking for ways to install the update on incompatible smartphones.
RustyGrom is a member of the XDA Forums and it seems he has discovered a way to upgrade the Lumia 1520 to Windows 10 Technical Preview for Phones.
Before we go into details, we should mention that if you are considering upgrading, you should proceed at your own risk as you will not have official support from Microsoft if something goes wrong.
If you still want to proceed with the hack after this, it would be good to know how it works. The upgrade is possible with the FiddleCore app that monitors traffic and blocks the Microsoft WPflights server that controls the Insider application, which is necessary for installing a new version of the operating system.
The Insider app allows users to edit registry information, so it's possible to change your phone's model and location. Keep in mind that smartphones made by manufacturers like Samsung or HTC will need completely different settings to install Windows 10 Technical Preview for Phones.
Follow the steps:
1. Reset your Lumia smartphone using Windows Phone recovery. Don't do any settings (you don't even need to log in), but wait until the end and restore when you have Windows 10.
2. Install the Windows Insider application on your phone.
3. Run the application, and from the about options, take a screenshot of your settings, because you will need it later.
4. download and install the WPInsidersHacks on your computer.
5. Run the WPInsiderHacks application on the computer and make sure to give it access to bypass the Windows firewall.
6. Then, connect to the same Wi-Fi network that your computer is connected to and edit the settings for the Wi-Fi connection by enabling the Proxy that will use the computer's IP address and port 8877.
7. Open Internet Explorer on your phone and type the address
https://[pc.ip.add.ress]:8877
where [pc.ip.add.ress] is the IP address of the computer running the WPInsidersHacks application.
8. Click the link at the bottom of the root certificate
9. When prompted, click to install the certificate, and then click OK to confirm.
10. Run the Windows Insider app and tap “Get preview builds.”
11. Select the custom action you want to run (for example Set to ATT Lumia 635 and click the arrow at the bottom.
12. Accept the window that will open and check the box at the bottom (the application should close).
13. Make sure you have correct proxy settings and run the Insider app again.
14. Once again, tap “Get preview builds” and sign in with your Microsoft account.
15. Go to your phone's settings and check for updates. If you're lucky, Windows 10 Technical Preview for Phones will appear and you'll be able to install it. Note that in some cases, you'll be asked to install Windows Phone 8.1 first and then Windows 10.
16. Finally, go to Settings and do another reset. Then, connect to the phone and let it restore your previous data.
This method has been tested and works on Lumia 1520 and Lumia 635.
