Yes! I have 2 dozen numbers "blocked" on my iPhone but the robocalls keep coming. I wish there was a "Report Spam" (Gmail) equivalent on iOS that employed smarter rules so I didn't have to manually blocking one number at a time (that's likely a throwaway account anyway).
Twilio will even let you spoof “your own number” on their network for outbound calls as mentioned in the article. Yes, they at least verify the number is “yours” before doing it, but it’s not hard to get around that limitation either assuming you have access to the other person’s phone.
Networking of all times has been grossly permissive historically and a lot of it is still today. With a lax upstream bandwidth provider, I could even pretend to have your IP address quite effectively (well, I don’t know a way to get just yours, but I do know how to get yours and the adjoining few hundred next to you).
From what I've tested, T-Mobile and Verizon will both fail to deliver SMSes that aren't originated by the carrier listed in the SMS routing for a phone # (which is wholly separate from the PSTN routing of a number, and can be a source of problems when changing cell carriers).
I can hijack SMS routing entirely for inbound/outbound, but short of doing that I can't forge the from field and get the message delivered.