Quite a few people are tackling DEBIT payments in innovative ways. Off the top of my head there's BankSimple (still in beta), ThinkComp (doing payment thru mobile along w/ their proprietary device), and another that I can't remember that does payment authorization using the audiojack from your iphone.

But if you're talking of supplanting the actual CREDIT industry itself(i.e., replaceing VISA/Mastercard), that's a pretty tough call. The industry is heavily regulated. In fact the credit card industry was borne out of regulation. It's also no small feat to deal with issues such as fraud, defaults, etc...