In Germany it probably is, technically. It's of course unlikely to have consequences for the individual user (I'm only aware of a single court case regarding Whatsapp doing the same, and that wasn't even a privacy case at the core), it's more something people are going to go after the service for. You are sharing private data with a company that you haven't been authorized to share it with, and non-registered users have no agreement with the company of their own which would allow it.