Napster changed the music industry forever and caused the music industry to (at least to some extent) change.
My thought is that proximity payments + API for banking system (ie: PayPal or Google equivalent) would shake things up for the banking industry.
In other words, if you could completely bypass the big banks - while they struggle to implement 10 year old payment system technology, not to mention high service fees - you'd end up with a system that is more convenient and manageable.
My point wasn't the file sharing aspect of Napster. It was about how Napster changed an industry.
Proximity non-card payments will change the situation for the debit/credit card operators, and possibly to a degree for Paypal-like services. Big banks are here to stay, and if they change something, it'll sooner be reasonably priced wire transfers to cut out the Paypal/cheque alternatives from hell.
To some extent, the card is where the control is. PayPal knows this, which is why they came out with a debit and credit card.
If a proximity payment service emerged that could interact with the API inside a device, it is a matter of time before a "simple, affordable microtransaction" service/app comes about. From there, exponential growth due to the order of convenience and simplicity. Banks, meet your "Napster", as it were.
Imagine mint.com came out with a proximity payment system for all devices and used the existing mint.com system as your "Bank Account" overview. Simply amazing!
Phones will replace credit cards.
I have a friend who works in IT for a fast food chain. They are gearing up for the iPhone5 among others. Drivers will be able to place their order on the highway for the next franchise location. When they arrive, they waive their phone at the proximity payment box and collect their food. The phone acts as both a payment method and a loyalty card with user history data down to the 'no mayo on the fish sandwich.'
(Yes, that is sarcasm.)