Right, so glad that everyone is still on AIM, ICQ, or even, BBM. They had huge networks, and barely anyone uses them now. This market has proven multiple times that users will switch and it will happen suddenly.n especially if whatsapp tries too hard to monetize them.
You couldn't possibly compare Gmail or Facebook with Whatsapp.
For many people, their Gmail id is their sole or primary id on the internet, used to identify them to scores of websites. It is their official online point of contact for various aspects of their online lives including their career, banking, social networking etc.
Facebook is their online social profile, which they spent thousands of hours curating.
Your Whatsapp id is merely your Phone no., (which was Whatsapp's main selling point). All interactions in Whatsapp are ephemeral in nature - Most people delete their conversations when their phone memory gets full. Compared to gmail and facebook, the switching costs are practically zero.
