Coming this CES (which is actually next week): a complete credit card transaction accessory and service for your iPhone. If this thing works as expected, you might actually see it in more than a few places (think: street vendors that will take credit card payments). A company called Mophie is planning to show off an add-on that works with an app to deliver credit card payments through Square, a payment service recently started up by Jack Dorsey, a Twitter alumni. This is one of a couple such systems that will be vying to fulfill the function (and probably take a few cents from each transaction for their troubles), but so far all we've really got is demos, no actual releases planned.
But maybe we'll hear more at CES. There's all kinds of applications here -- a solid, working implementation of a service like this could end up being extremely popular for anybody that regularly needs to conduct transactions out in the field.