How to install WhatsApp on an iPad 4 without 3G?
From the FAQ on whatsapp.com:


  Other devices are not supported at this time. If you try to download WhatsApp on an unsupported device, you will receive a message that your device is not supported and you will not be able to download WhatsApp. We currently do not support tablets, computers, or Wi-Fi only devices, and do not plan to do so in the foreseeable future.