It does in my case. I have a few hundred numbers blocked and I get a call maybe once a month. I block my own number.

You sure it wasn’t just a single digit off from your phone number? I’ve never gotten a call from myself. Is Caller ID that insecure?

Yes, it’s that insecure. I used to freak out friends in the late 90s doing it, but sadly it’s not changed much and is just as easy as ever.

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).

Yes. The number is just a property and can be pretty much anything. Same goes for SMS, by the way.

Sign up for any random SMS API service. You'll note that you can send SMS using anything you like as the 'from' field. There's no checks or restrictions. Same goes for voice calls in most cases.

Which ones actually support this?

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'm using the noname brand resellers, not the carriers themselves. I guess that's why.

I've tried a dozen thus far to no avail :c

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.

Hmm maybe it has changed recently...