Windows 10 Mobile upgrade is free, if your Windows Phone 8.1 is eligible for the upgrade, you should definitely install Windows 10 Mobile in your device. Btw if you upgrade to Windows 10 Mobile and later you decide to rollback to previous Windows Phone 8.1 operating system, you can do this using Windows Device Recovery Tool.
Why Windows Phone users are now a serious security risk to Jul 12, 2017 Download Windows Phone 8.1 ROM Now to Roll Back from If for any reason, you feel that Windows Phone 8.1 was much smoother for you, and you still need MS to fix few bugs, here is how you an roll back to Windows Phone 8.1 later from Windows 10 Mobile. Post Windows 10 Mobile roll out, all Windows Phone 8.1 ROM will not be available any more. Windows Phone - Wikipedia In 2014, Microsoft released the Windows Phone 8.1 update, which introduced the Cortana virtual assistant, and Windows Runtime platform support to create cross-platform apps between Windows PCs and Windows Phone. How to Downgrade Windows 10 Mobile to WP 8.1 | MobiPicker
In 2014, Microsoft released the Windows Phone 8.1 update, which introduced the Cortana virtual assistant, and Windows Runtime platform support to create cross-platform apps between Windows PCs and Windows Phone.
While Microsoft has promised that any Windows Phone running Windows Phone 8.1 will get the update, this doesn't mean they will all be eligible for the Windows Mobile Insider Preview. To check that
May 09, 2016
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