The mobile application "Mint" makes it possible to pay with your mobile phone and keep track of your spendings.
For example at the grocery store you can pay with Mint. The amount to be paid is sent wirelessly to Mint and you can select your preferred credit card or bank account:
You enter your PIN-Code and you are done:
Afterwards MintBudgeteer calculates your new budget and shows you how much money you have left to buy stuff:
This scenario and the images are taken from a presentation by John Pettengill. He states that future mobile internet should not just be the internet on a smaller screen. The presentation is embedded below. The scenario starts at slide 60.