Already existing Contact-less Credit cards are working based on radio frequency identification (RFID) which is basically one-way communication system.
This RFID was initially devised during Second World War for distinguishing friendly air crafts from enemy aircrafts.
Now, RFID tags are used in many fields such as retail stores, shipment tracking, identifying people and animals.
NFC(Near Field Communication) is the improved version of RFID. It will be two way and bio-directional communication system.
So it will help to improve the security when using cellphone as Credit Card.
Mobile user location data and IP mapping can be used to make sure whether the cellphone (I-e credit card) is used genuinely.
These NFC mobiles can be used as Door Keys and Theater Tickets also.
It seems already some banks in New York are implementing this NFC system in trial basis.