[ssfrr]

This was last week. It seems like the same mechanism though, if the phone is still tied to their Apple ID.

[pfranz]

I wonder if the only part that changed is now the have a user-facing way to deactivate: https://selfsolve.apple.com/deregister-imessage/

iMessage was launched in 2011 and archive.org shows that page first showing up in late 2014. I remember hearing very few options for removing your old phone early on.