virtualbox.org

My question is not about "Which changes trigger reactivation in a Windows guest?" ( viewtopic.php?f=2&t=22653 )
But how to install windows product without the need of reactivation.

On my Linux box, I use to use windows xp on a VM for a specific software. I decide to test it on windows 10. This Linux box had never seen windows. To make my test I use the DVD re-installer software from a friend of mine ( same pc vendor : Asus ). So I reinstall every thing with a dual boot "Windows + Linux".
Then I upgraded to windows 10 and made my tests.
As every things work, I decide to buy a windows 10 license.
I removed every things one more time and reinstalled Linux.
Then I installed Virtualbox.
Then I installed windows 10 on a VM.
At the beginning, I have been asked for a key. Then I typed the key that I bought and received by email.
After finishing the install of windows, I installed virtualbox guest addition. Then I saw that windows was not activated. When I tried to activate with my key, this one is refused with error code 0xC004C008 : The activation server reported that the product key has exceeded its unlock limit.
The internet key vendor told me to make a phone registration.
I did that with success.

So my question is : How to do a clean install without phone activation.
It seems that installing virtualbox guest addition make a new hardware.

This has nothing to do with Virtualbox.
The answer is very easy: Buy a legal key from an official Microsoft reseller.

Installing Guest Additions gives drivers for the virtual hardware the OS was installed on. I don't believe new hardware is provided. Installing GAs should not cause reactivation.
MS's online activation servers may have made a mistake, but assuming one follows the EULA one should be able to get phone activation to work. (Of course the ability to activate depends on the legitimacy of the license and the internet seller, which might be the reason why you had to phone-activate.)

I'll put it more forcefully: installing the Guest Additions does not change the activation status of a Windows guest OS. We would already know if it did.

Either you were mistaken about the original activation (and it in fact failed), or you changed something important in the VM recipe after activation, or you did something like clone the VM or create a new VM around the existing disk, either of which will invalidate a Win7 activation. Moving the VM to a new host might also cause deactivation, though usually that would be in combination with another VM recipe change.