This is very easy and cheap to implement with Asterisk and a no-name VoIP provider. I've done some messing around with phones in the past and I would expect that Twilio has little/no effect on this space -- the barriers to being spammy with Twilio are higher than with Asterisk and another VoIP provider.

Not at all. There's dedicated dialer programs, and they use much, much, cheaper providers than Twilio. Dialer wholesale companies make around 10% if they're doing well. It's a very high volume business, and they are constantly on their feet since other providers will cut them off if their call acceptance and durations aren't high enough.

Telecom makes most "web scale" stuff look very small. Even a one-man operation might be doing 4000 calls a sec, each requiring about 20 packets, plus routing and billing lookups and records.

I think those things were going on long before Twilio got in the game.