An American mobile application consultant has launched an experiment that lets people download a picture of his Starbucks card to their phones and buy coffee with it.
Jonathan Stark says his 'Jonathan's Card' is an experiment in social sharing of physical goods using digital currency on mobile phones.
People in the US can save a picture of his 'card' on their phone and hold it against barcode scanners in Starbucks' outlets to pay for their coffee with his account.
Stark has also set up a Twitter account that provides an update every time the card balance changes so people can check to see if there is enough money on it before visiting the coffee chain.
The developer is asking people to tweet about what they buy, adding pictures and users can also add money to the card "and enjoy some serious good karma".