Name, address, and phone number served plenty of critical functions when they were published in the White Pages. Cell phones not being listed there was kind of an accident of history. It was common to call a listed landline and be given or forwarded to a cell number. Only after most people stopped having landlines altogether did a phone number come to be considered sensitive information (unless you were a celebrity or something).

Ironically Facebook is responsible for much of this, as friending someone on Facebook became a lower stakes, less intimate alternative to exchanging phone numbers.