Apple Thoughts: Share Your iPhone 4 Data Plan With Your iPad, if You Dare

"You can't argue that having 3G everywhere on your iPad is unbelievably convenient. This ubiquitous access to all the content you want is indeed nothing short of revolutionary. Unfortunately, the convenience comes at a price."

So yes, you can fit your iPhone 4 Micro SIM card into your iPad and by inputting the above credentials into the APN Settings fields (go to the settings app, then preferences ---> cellular data) on your iPad, but in the process you do violate the AT&T terms of use and risk the wrath of AT&T. But if you feel lucky, you now know what you need to do.