Reports suggest Windows 11, and likely older versions of Windows, can no longer be activated while offline.
Microsoft has seemingly disabled phone call activation for Windows 11, and perhaps older versions as well, making it impossible to activate Windows without an Internet connection.
This is an unwelcome development for users that want to airgap their systems and enthusiasts who want to activate older versions of Windows on retro hardware. There are some conflicting reports which suggest that select regions may still offer phone activation, but for users in the United States, early reports indicate other Windows versions are impacted by this change as well.
Ben Kleinberg suggested phone activation was no longer possible in a Dec 18th YouTube upload, where an attempt to activate Windows 7 failed.
