What an excellent idea… Transactions is an iPhone app that allows anyone to accept Credit Card payments wherever they have a wifi, 3G, or EDGE connection. It works in conjunction with PayPal Pro or Authorize.net accounts.
They make 2 versions of the app. The full (unrestricted) version costs $29.99. But, there’s a free (lite) version that has the same capabilities, but it limits you to 2 transactions every 12 hours.