So we used it for the first time this week.  A simple and small credit card swiper for the iPhone.  It is small device that plugs into an iPhone or iPad and allows you to use their iPhone app to swipe and receive credit cards.  If you run a boutique or sell produce on the corner, this is a quick and easy way to start taking credit cards.  The setup on their website: squareup.com is easy and free.  Even the swiper will be shipped to you for free. Your only cost is the 2.9% or so transaction fee.