Do they actually need to purchase numbers to do that, though?

I always imagined that there are certain shady providers ("grey-market Twilio" sort of idea) that just let you run single outbound call/text requests through a giant pool of numbers shared with other customers of the service. Perhaps specifically a bank of residential numbers plugged into banks of regular cell phones, like a residential IP proxy service provider.

Somebody at some point is purchasing them, probably not the spammers/scammers themselves.

It's very unlikely anybody is placing spam/scam calls with regular cell phones when VoIP numbers are easy and cheap to get, and when VoIP systems are far easier to manage.

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