Neither WhatsApp or Facebook can read the messages we send, but from now they will know our phone number. That is, the Facebook application can use your number WhasApp and vice versa, mainly to allow advertisers to know your audience and send more specific messages. Guaranteeing anonymity. At this point they are very clear:
We will not publish or share your number with other WhatsApp or Facebook. Not sell, share or give your number to advertisers.
The number of WhatsApp also serve to improve the suggestion of friends. From now on if you have in WhatsApp, Facebook certainly can add you to more easily.
Fortunately, we have 30 days from the notification reaches us to prevent WhatsApp share information with Facebook. When we see the message we give to read more and uncheck the box.
Many users will see on this policy change a reason to distrust WhatsApp, but the idea is that an application billion active users is important enough to not use Facebook within its ecosystem. Privacy guaranteed content will, but the advertising pie is too large and requests generate income.