innerfence has developed an iPhone App called the Credit Card Terminal. It is a thin application that acts as a front end and uses an Authorize.net Merchant account using the Authorize.net API over SSL. Looks pretty neat and a useful option for mobile acceptance of credit cards.
Looks like innerfence is a Authorize.net reseller, since you can use any authorize.net merchant account – I suggest you shop around the the best rates, theirs appear to be a little high.
I’ll put this in the "Why didn’t I think of that ?" category.