For any artist or musician who has participated in a street fair, one of the thorny problems is accepting credit cards. You can bring a standard swiping device, or process it on paper or not acceptr them at all. Moreover, if you are just getting going, you have to sign up and pay a startup fee to get going.

But a company called Square (www.squareup.com) has introduced a gizmo and a method for using your cellphone to accept payments. The process is: go to their site, sign up (free) and they will send you a gizmo to plug into your phone. Once you are setup you can begin accepting credit card payments right away. 

I tested mine today while riding the train. I was able to charge a credit card thru my phone while riding the commuter rail from Lincoln to Boston. They take a percentage of the deal 

Square's card processing fees are:

2.75% + 15¢ for swiped transactions

3.5% + 15¢ for keyed-in transactions

There are no activation, gateway, monthly, early termination, or hidden fees.

No limits on transaction size.

Check out this video which shows the gizmo in action...