If you’re not opposed to ripping your iPhone open and putting an NFC enabled credit card (such as the Tap & Pay card from the Bank of America) between the battery and the casing, then perhaps this could very well be the hack that you would be required to perform if you wish to make your iPhone NFC capable.
It looks like a pretty cool hack although we’re not sure if the majority of iPhone 4 users will be willing to mess around with their shiny new hardware, but if you’re up for the challenge and you know what you’re doing, Unplgged has the details of what you would be required to do in order to gain NFC function on your iPhone.