[tw04]

>with data that most users do not provide to FB.

And you're basing this on... what? Facebook nags you EVERY TIME you login for your phone number. EVERY TIME. I can tell you every last one of my friends who is non-technical has put in their phone number simply to get rid of the nag message. While my evidence is anecdotal, it flies in the face of yours. So I assume you have a citation for your "most users" comment.

[parthdesai]

So i did some search. Facebook app is installed 1 billion - 5 billion times on android alone. Facebook app has access to your contact card, your contacts and bunch of other stuff. Now let's say there are 20% of people who review these permissions and don't give fb access to everything. Even with that it leaves ~800 million apps with access to phone numbers. And this is Android alone.

I would be pretty surprised if evgen had same views if he wasn't working at fb.

[evgen]

Have left and have been working on my own startup for several months now, but I am aware of how some of the data is siloed at FB and also that WhatsApp was run very independently (as in, almost no operational contact between the two companies) up until the summer at least. I don't doubt that FB can tie a specific FB user id to a WA user id, and if they tried hard they could tie a large fraction together using a variety of data sources (certainly not a 'one-line SQL query') but between 10-25% would fail due to bad data on either the FB or WA end. A partially complete data set is not as useful as you might think...