I am going to buy my first smartphone samsung galaxy S4 android (first time smartphone user) and install and use whatsapp or viber.

I read that whatsapp/viber will automatically add all the whole contacts list and all my contacts who have whatsapps/viber will be able to see me on their phone.

I have many contacts that I am not close and seldom contact them, I do not want them to be added to whatsapp or viber. How can I do that? Is there other apps that can do that?

I understand that there is a block function, but I do not want to use it to block them because if they are added to my whatsapp/viber and then after that I block them, I think they will know it because I have added them and I am never seen online on their whatsapps/viber. I do not want to add them at all.

Viber told me the only option is to delete this user from the contact list.