I have a radical solution - it should not be possible to contact someone unsolicited.

All phone calls, SMS, emails, and instant messages should be blocked unless the other party is in my contacts or I have reached out to them first (plus opt-in contact from contacts of contacts, etc). Ideally, cryptographically verified.

I would argue this is the real solution to spam and scamming - why on earth are random people allowed to contact me without my consent? Phone numbers or email addresses being all you need to contact me should be an artifact of an earlier time, just like treating social security numbers as secret.

I realize this isn't super practical to transition existing systems to (though spam warnings on email and calls helps, I suppose, and maybe it could be made opt-in). I dearly hope the next major form of communication works this way, and we eventually leave behind the old methods.

Also, SMS shouldn't be used for 2FA anyway.