You have an iPad or a second iPhone and would like to send messages from there? TwoApp allows you to pair this device to your Whatsapp number whilst presenting you a native user interface. Scanning a QR code is everything needed to set it up!
Having your iPad in your hands but your iPhone is upstairs? Just launch the app on the iPad and you will be able to interact with Whatsapp no matter where your iPhone is - it could even be in another city and you would still have access!