[parthdesai]

And that's why i said users who have listed their phone number.

They can get phone number from users who use their phone number to log in but not have listed it in their profile (me), people who have enabled 2FA or from messenger. It's just a simple sql join. Ofcourse not at FB scale but this is me thinking about this problem for 10 seconds and also i'm in probably not even as intelligent as the dumbest guy working at fb.

[pzh]

And then there are people who just use a Google Voice number on Whatsapp instead of a real phone number, and many don't even have a phone number listed on Facebook. I'm actually surprised that anybody would give their real phone number to Facebook, Whatsapp, or any of the other "social networks"...

[hobarrera]

> I'm actually surprised that anybody would give their real phone number to Facebook, Whatsapp, or any of the other "social networks"

The only use for my phone number is registering for stuff like WhatsApp. Why would I want one if not for stuff like that?

(note: talking about the number itself, not a smartphone. I use a smartphone for lots of other stuff)

[pzh]

But you can give Whatsapp a Google Voice number instead of your real phone number. That way if they decide to sell it as part of your profile, you can easily change/cycle it (or apply better filtering, DND, etc.)

[hobarrera]

AFAIK, Google Voice is only available in the US, and this trail is in the EU.

[TeMPOraL]

2FA + the very fact that many - myself included - use Facebook, et al. primarily on a smartphone.