There's one missing piece in that article, and it's the CNAM database (US only).

CNAM is the database that carriers use to give you alphanumeric caller ID ("SMITH JOHN" instead of "+1 (555) 123-4567"). Many carriers don't display this data as far as I believe, but most of them make it available.

Querying that database isn't free, but you could probably find a way to do it for a few hundred numbers relatively cheaply. People's names and emails are often similar, so you could probably figure out an algorithm to give you the most likely candidates.

The data is often wrong in interesting ways (I've seen everything from deadnames to people's exes they still share a plan with), but it is still pretty useful.