[chatman]

Is there a legal way to stop Whatsapp from sharing my address book with Facebook?

[brandnewlow]

Why do you think Facebook just paid $19b for them?

[enscr]

Valid point. I hope a lawyer can weigh in.

[steveklabnik]

http://www.whatsapp.com/legal/

"In the Event of Merger, Sale, or Bankruptcy"

You already gave them the right to share the information. (IANAL)