> Doctor's office calling to confirm your appointment; restaurant confirming a seat reservation; delivery guy is outside and can't find your doorbell; Lyft/Uber

> Doctor's office calling to confirm your appointment; restaurant confirming a seat reservation; delivery guy is outside and can't find your doorbell; Lyft/Uber/whatever is nearby and is looking for you; pharmacy calling to inform about a prescription being ready; some store calling to inform that your order is ready to be picked up; insurance company calling about some claim; etc. The problem is phone number that is short and easy to guess. Imagine replacing them with a longer token that would be generated each time you want to give someone else a way to contact you (e.g. displaying a QR barcode on your phone and letting the other party scan it). Then you'd share a unique identifier with all that parties. Delivery guy can get a token that expires after a while. If someone abuses their ability of contacting someone, the token would get revoked. I leave the details and implementation as an exercise for the reader ;)