In Germany, it is.
Relevant quote from the Whatsapp TOS (Whatsapp belongs to Facebook):
> Address Book. You provide us the phone numbers of WhatsApp users and your other contacts in your mobile phone address book on a regular basis. You confirm you are authorized to provide us such numbers to allow us to provide our Services.
Relevant german court order:
http://www.lareda.hessenrecht.hessen.de/lexsoft/default/hess...
It's a bit lengthy (and difficult!) to translate. In summary it's a child custody case about excessive smartphone use in which the court orders the mother, among others things (limiting smartphone usage) to get written consent from all contacts in the child's addressbook. The issue is that in Germany, your contact data is "copyright" be yourself. You don't have to put up with people freely resharing your contacts and theoretically, the child could have been "sued"(+) by anyone in the addressbook who isn't also a Whatsapp user.
(+) There is a "light version" of "sueing someone" in Germany, called "Abmahung", which is frivously used by some law firms.