First shown off at Macworld, the Square dongle is a small peripheral that allows any iPhone to easily accept credit card payments and is currently being tested by Adafruit. This can mean big business not only for its creators but also for every small business owner in the world, as an iPhone and peripheral would presumably be much less expensive to implement into any small business environment. Not to mention the fact that it makes mobile businesses much more flexible, allowing them to cut costs and boost productivity. See below for a link to a video of how the peripheral works.
Of course there is an app to accompany the peripheral that allows for the processing of the payment as well as input of the customer’s signature via the iPhone touch screen. While the entire app and technology is still entirely in a beta stage, it might not be long before you see these types of peripherals hitting small businesses, street vendors, and other mobile businesses.