Yesterday, there was an article on HN about the plague of Payday Loan scammers who prey on gullible people. The comments talked at length about how difficult it is to get off a call list once your number is known to these people.

Why do we need publicly accessible phone numbers, i.e. phone numbers that anyone can call?

Prediction Time

In the future, we’ll have one-use unique identifiers (numbers) that we’ll generate ad-hoc whenever we want to share our contact information with a new person. Met someone at a party, want to exchange numbers? Pull out your phones, touch them together, you’ve generated a public/private key-pair for contact with just that person.

This doesn’t need to be necessarily encrypted, just a way to authenticate that the person is allowed to contact you. That you can also encrypt communications to that person using your public-key cryptography is a bonus.

If it...