Unrelated to your comment but relevant: I had my friend's number saved on my phone, but we were not in touch for over an year; one day I installed WhatsApp and saw him there - I pinged him; the response came, "Who the fk are you, you b*d! There is no <my friend's name> here. Go to hell!!".

Turns out my friend had changed the number, so the cell number was released and assigned to another user after few months but WhatsApp on my phone thought it was my friend on the other side.

That was when I knew WhatsApp is not revolutionary, it's just lazy, convenient and famous.