How can I use an iPad Mini wi fi only on 3G using my iPhone ?

I have been told by another iPad user that with an iPad mini or even any iPad that is wi fi only,they can be used on a 3G network using an iPhone as the router.
Is this correct or is there an App needed to do this ?

Data charges then are charged to my iPhone Network Telco account.

This sounds like a good idea as I do not have a 3g or 4g iPad or iPad mini.