WhatsApp to Share User Data With Facebook to Show Targeted Ads
By coordinating more with Facebook, we'll be able to do things like track basic metrics about how often people use our services and better fight spam on WhatsApp. And by connecting your phone number with Facebook's systems, Facebook can offer better friend suggestions and show you more relevant ads if you have an account with them. For example, you might see an ad from a company you already work with, rather than one from someone you've never heard of.
Existing WhatsApp users can choose not to share their account information with Facebook. On the iPhone app, before you tap "Agree" to accept the updated terms, tap on "Read," scroll to the bottom, and toggle the control. Users that agree to the updated terms also have an additional 30 days to opt out by going to Settings > Account > Share My Account Info and toggling the appropriate control in the app.