Apple is planning on introducing NFC, or “Near Field Communications”, in the next generation of iDevices. This means that users will be able to pay for purchases at NFC-compliant kiosks using their smart phone as an authentication token.
It will be interesting to see how Apple secures this functionality; I would hope that there is some sort of PIN or other unlocking required. Otherwise, losing a phone would be equivalent to losing a phone and a credit card. In fact, since NFC payment is generally a direct bank account debit rather than a credit transaction, it would be even worse.