Microsoft is working to bring the Windows 10 Technical Preview to as many phones as possible, but currently here is the list of phone supported to test the first preview of Windows 10:
Lumia 630 Lumia 635 Lumia 636 Lumia 638 Lumia 730 Lumia 830
Also, as previously announced by the company, the Windows 10 Technical Preview for phones will include a roll back feature, which is similar to what the desktop of Windows 10 offers to allow your phone to go back to the previous version of the operating system if things aren’t working or you simply want to opt-out of the program. Remember that you’re getting a work in progress piece of software, as such make sure you understand what you’re doing; things will not work flawlessly and a lot of feature aren’t included. However, the version of Windows 10 Microsoft is making available today should give us a glimpse of what is coming for Windows Phones. All content on this site is provided with no warranties, express or implied. Use any information at your own risk. Always backup of your device and files before making any changes. Privacy policy info.
