The Square is actually giving out the reader for free believe it or not. The thing you have to pay for is the actual transactions which are very competitive at just 2.75% of the transaction and $0.15 for all credit cards. I'm positive you could find a variety of ways to utilize a service such as this. It also seems like it would be a really nice option for businesses or for people that do merchant selling online, but they don't want to have to deal with payment processors like Paypal, and they don't want to deal with less trustworthy options like checks!
Download Square Mobile App for iPhone or Nexus One or Droid.
Check out the below video for more info: