Yes, JioPhone is a dual sim mobile phone. You can use one 4G sim card and one 2G sim card.
Unlimited. JioPhone comes with 4GB Internal Memory - so, you can store as many contacts as you want, depending on the free memory on the phone.
No. JioPhone does not support WhatsApp at least for now. In future, it may support.
The standard packaging of the JioPhone includes Mobile Phone, Battery, Charger and Quick User Guide. You will not get earphone inside the box.