nSquareup is an mobile credit card payment service currently available for iphones, ipads and android mobile phones. With a small credit card swipe installed to the iphone’s audio jack it allows users to accept credit cards, process credit card payments and even accept signatures.
Square founded by two internet pioneers Jack Dorsey;cofounder of twitter.com and Kevin Rose founder of popular social news site Digg.com.
Squareup makes accepting credit cards very simple for small merchants and mobile professionals. All you have to do is go to squareup.com and create a new account. There are no monthly fees or contracts for this service. Once your account is setup you will receive a small credit card swipe for your phone for free.
Below is the payment structure and payment processing fees associated are taken from the squareup.com

Card-present (swiped) rate 2.75% + 15¢

Card-not-present (keyed-in) rate 3.5% + 15¢