Well, the Eye-Fi SD cards are SD cards with an integrated WiFi client. They are basically a cheap alternative to expensive WiFi add-ons for top D-SLRs and cameras that do not have that option at all. Basically you join a WLAN with the SD card and then all images will automatically be uploaded to a computer on the same WLAN or some online services without any need to transfer the images to a computer first. My understanding is, that the iPhone app will allow the iPhone to act as a wirelessly tethered computer with these cards, so you can e.g. download images from the camera onto the iPhone and then select/delete etc. and finally upload to an online service or sync to a computer. Since the old iPod camera connector does not work with iPhones, this would be a great alternative to use the iPhone for storage/backup during trips, especially once there will be models with more capacity. How much sense that will make when considering battery consumption (camera and iPhone) remains to be seen...