Use Activation Troubleshooter in Windows 10  

No, there's no option to activate by phone as this was a free upgrade. Free upgrades may not be phone activated (MS support statement), only internet activation. (by the way: sorry for not coming back earlier, I missed the last notification e-mail).

awesome, can still use this method after july 29?

Brink said:

Yes, if you have the digital license linked to your Microsoft account that you sign in to Windows 10 with. :)

thank you !! mr. Brink

I have upgraded my Windows 7 OEM to Windows 10. Does the following apply to my Windows 10? Can I still activate it after changing my motherboard?

'If you made a significant hardware change to your device (such as replacing the motherboard) Windows 10 might no longer be activated. If you're running Windows 10 (Version 1607) and added your Microsoft account and linked it to the digital license on your device, you can use the Activation troubleshooter to reactivate Windows.'── quoted from https://support.microsoft.com/en-us/...-10-activation

cereberus said:

It is not clear if this will work for an original oem licence. In anyy case, this violates the EULA.

I have been thinking the same.