What Options are there to activate Windows XP nowadays?
The "regular" methods provided with XP (phone and online) don't work anymore. The phone number is not valid for activation anymore (I tried the German one) and the online activation does not work either (in a quick test within a DMZ other protocols like ICMP or HTTP worked fine when I accessed an internet server).
The latest question/answer I could find here on superuser is this one: XP Activation and Dual Booting which doesn't provide an answer to my question. In addition the question asks only if it can be done in general not how (neither does the existing answer say how), and about other problems (dual boot), so I decided to post the question again as specific question just about the activation process.
The solutions can be a workaround (disabling the activation check), but for security reasons, it shouldn't contain a binary download. Preferably it also shouldn't require a network/internet connection. Although there is no way around using WinXP, I want to minimize security risks.
EDIT1: Since quite a few people asked, please note why (in my opinion) this question is not a duplicate of XP Activation and Dual Booting, please see my explanation above. I made a thorough explanation in meta here.
EDIT2: it was suggested to call MS support and/or sales unfortunately they do not help with WinXP anymore.
EDIT3: please be aware that running an outdated OS without security updates poses security risks explained here as BurceWayne points out correctly. Therefore, if possible you should change/upgrade the OS of your device. However in some cases it's not an option to change to a different OS, e.g. because certain drivers/HW/SW is only compatible with Win XP.
EDIT4: note, the activation process comes after entering a installation/serial key (e.g. from the licence sticker)