For all of you that have a smartphone with Win 8.1 you can now upgrade to Windows 10 (both of you ).
..If you have one of these phones:
- Lumia 1520
Lumia 930
Lumia 640, 640 XL
Lumia 730
Lumia 735
Lumia 830
Lumia 532
Lumia 535
Lumia 540
Lumia 635 1GB,
Lumia 636 1GB,
Lumia 638 1GB,
Lumia 430
Lumia 435
BLU Win HD w510u
BLU Win HD LTE x150q
MCJ Madosma Q501
Some features will be deprecated:
When you install the Windows 10 upgrade, some features currently on your device will be modified or removed, including the following:
Notifications for missed calls, messages and emails on contact tiles is not supported at the time of Windows 10 Mobile release.
Me Tile and Me Card are no longer supported.
Cortana can no longer search for apps, settings, email, text messages, contacts and QR Codes on the device and can no longer open apps through voice commands.
"Hey Cortana" is no longer available on some upgraded devices.
Group tiles can no longer be used to receive social networking status updates.
Indoor Maps are no longer available for some locations.
Certain enterprise features, including Data Protection Under Lock, are not available. Please contact your Microsoft Volume Licensing representative for more information.
At time of Windows 10 Mobile release Outlook Mail app cannot open .EML attachments.
The Outlook Calendar app does not support Tasks.
The MDM functionality to prevent saving and sharing Office documents is not supported.
The benefits of upgrading to Windows 10 are not that well described but future updates will be automatic:
Windows 10 Mobile is automatically updated. Windows 10 Mobile users will automatically receive updates during the support period when they are available.
From a privacy point of view; it is questionable if that is desirable.
More here
(Click the "Mobile" tab)