I read through How long will Microsoft support Windows XP Professional? but could find no mention of how long Microsoft will continue to allow/support activations of XP for, using internet or over the phone.
Windows – Will I still be able to activate Windows XP after support ends
licensewindows xpwindows-activation
Best Answer
I don't know about over the Internet, but the phone-activation option uses one number for all Microsoft products, and the last time I needed to use it it didn't ask which product the user was trying to activate. It therefore seems reasonable that the phone activation option will remain as long as Microsoft allows activation of any of their products over the phone.