And how do you think such a sync would work? To find the contacts in your phonebook that have Whatsapp, you need to have both datasets in the same place to do the comparison. So either you:upload your contacts to their server, compare there and send the results back to your phone download the entire Whatsapp user database to your phone and compare it on your phone to your address book. (obviously, that's NOT going to happen) Of course you could. By adding your contacts manually, like any other IM system does.