It seems as though if a group of people all had the same app installed on our phones--like Signal, or something similar--we could bypass the phone number system, and set up our own audio-chat sessions over the data connection. If anyone else wanted to talk, they would also need to have the same app, or use its API, and add my contact information. That would add quite a bit of friction to person-to-person communication, but I kind of want that now, as it would also add equal friction to robot-to-person communications. But it isn't exactly easy to get a mobile data network connection without also buying in to the phone network addressing system.
Everywhere I look, in the realm of security breaches and vulnerabilities, a large number of exploits use the public switched telephone network, or its addresses, to compromise the security of the people forced to use them by network effects. Many of the others exploit email addresses on the large providers--apple.com, gmail.com, yahoo.com, hotmail.com--which are popular due to ease of use, and the difficulty involved in getting mail delivered from a private domain to someone using addresses from those providers.
I get the impression that if I set up a phone to ring on a SIP request to 'email@example.com' instead of something like 'firstname.lastname@example.org', it would never get robo-dialed calls. But it would also never get calls from people I might want to speak with, because their phones can only call phone numbers. What's the way out of this trap? How do we stop jackasses from jumping into the middle of any private communications we might wish to have, in a way that is also easy enough to use that nontechnical relative can use a prepackaged setup for it?