TUAW tells how to use an unlimited iPhone 4 3G data plan from AT&T on an iPad.
Maybe I'm less frugal than most, but I have unlimited plans for both and don't really think that the extra 30 dollars a month is wrong to pay. Why? Well for starters I understand how AT&T needs the money. I mean, despite their record profits the network needs all the cash they can get to build out more infrastructure, so I figure, give them some additional help, for the upside down the road. Better bandwidth. With their ONE Network approach backhaul issues have to go away. Same for logging on, and at some point they begin to rival the cable companies with their own flavor of Triple Play that goes beyond uVerse.