As an admin for Charcoal, the team who develops Smoke Detector as a volunteer effort, I'll pipe in to mention that we can always use more volunteers. This spam wave is not confined to Server Fault, though yesterday's deluge by and large was. A simple way to help is to join the Charcoal HQ chat room and flag the spam as it's being reported there, in near real time based on a battery of regular expressions and other detection techniques.
If you can analyze the archived spam and help develop better detection rules, that's obviously a very valuable sort of contribution. Authorized users are also encouraged to !!/blacklist any new phone numbers we don't currently detect, though you need to be an enrolled team member with some amount of participation in the project before you can be granted these privileges. Perhaps see also our guidance at https://charcoal-se.org/ if you are interested in taking part.
(Our general guidance calls for several confirmed spam reports before we blacklist anything, but this particular campaign is far above and beyond anything we have seen before, and so we have relaxed the blacklisting criteria for this particular phone support spam campaign.)
I'm also wondering what is being done socially / politically to seek restitution for this serious DoS attack. Perhaps somebody from Stack Exchange could fill us in on whether they are seeking legal remedies and what sort of evidence or coordination would be useful for that. We archive the spam in metasmoke as soon as it's reported, so we may have information which could be useful for any fact finding. (However, we don't have access e.g. to IP addresses; we simply use the features of the existing Stack Exchange API.)
For fun, here's a screen shot of the chart on metasmoke's home page just now. You can clearly see that yesterday's spam levels were quite extraordinary.
