Skype for Business vs. Whatsapp

1. With whatsapp people may chat with anyone who has whatsapp application. And whatsapp is free. For people it's easier to communicate via whatsapp. S4b is paid. You may communicate only with companies that uses skype for business, and only if your administrators configure federated trust with that company. S4b is used only within one organization, but people need to communicate other people who don't have S4b. There is no solution to add people who uses free IM messengers, but skype. However, with S4b you are able to communicate only with "microsoft account"-ed skype users.

2. S4b doesn't support chat on mobile devices. Nowadays you can't find person who doesn't have a smartphone. I don't understand why microsoft didn't implement chat on mobile devices.

3. whatsapp disadvantage is only in conferences. whatsapp don't have them at all. S4b has a desktop, powerpoint sharing, and usefull conferencing tools. You may even invite a person outside of your organization, who even don't have S4b application. He may use guest account via browser plugin.