From what I remember, you can change in and out of phone numbers like with Google voice - and there are a ton of them. I don't know if that matters for spammy calls - I don't know anything about that domain.
Twilio allows you to automate calls programmatically, and what a lot of the callers do is wait for you to say hello - they're robo dialers. I wonder how much Twilio has influenced that (unknowingly or deliberately)
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.
Twilio allows you to automate calls programmatically, and what a lot of the callers do is wait for you to say hello - they're robo dialers. I wonder how much Twilio has influenced that (unknowingly or deliberately)