Microsoft deactivated the offline telephone activation back in december last year. But now in my current project we need to activate Windows Pro and the Office Suite in an offline enviroment. Microsoft established a new process which I think is working pretty good.

At first I read that the offline activation is not possible anymore for OEM licenses, but in the documentation page for the new activation process states that it is possible to activate Retail, OEM and Volume / CSP licenses in this portal.

The last catch I encountered were that the activation is only possible at the CLI - at least for the OEM license. I tried to enter the confirmation ID that you get from the website over the GUI where the telephone acitvation where in the past, but I after entering the ID it would fail.

The only way it worked for me was to enter the confirmation ID over the CLI with the command: slmgr /atp <confirmation-id>.