[ejain]

Pretty much all ToS have a clause that states that the terms can change any time. Where services differ is whether they'll provide you with advance notice (or if you're expected to check for changes yourself!), and if you are able to close your account and have your data removed (I believe this is required in the EU).

Looking at http://www.whatsapp.com/legal/, it appears that WhatsApp falls into the "we can change our terms without letting you know" category, and I don't see anything about their data retention policy :-(