Many companies present you with the opportunity to "Protect Your Account" with SMS, and for that protection they 'just' need your phone number. Turns out the p

Many companies present you with the opportunity to "Protect Your Account" with SMS, and for that protection they 'just' need your phone number. Turns out the phone number is the best unique identifier and is the perfect key for joining up lots of disparate sources of data. It's the kind of thing that you could either sell directly or use as an index to determine things like your estimated income. It wouldn't surprise me if Facebook has had multiple technical methods for devising/stealing and disingenuous "protect your account" campaigns for willingly turning over users phone numbers.