Re: Using a QR code image...
"If the CurrentC app shows a QR code image that is effectively your payment details,"
I thought the idea was that the app scans QR codes on products, popping up information on screen (price, etc) and giving the user the option to make a payment. As such, it sounds (er... sounded?) marginally better for anyone worried about NFC-based systems leading to accidental payments - only marginally, though, because there would still be a risk through phone theft etc, so is still naff overall.
If, however, it holds the user's payment details in a QR code that is presented to the retailer, then what you've described is a big security fail.
But also, if that's how it works, I fail to see the need for a special app - and therefore why Windows Phone and Blackberry can't be supported: they're perfectly capable of displaying images!)
Afterthought: Is it a one time QR code generated at the time the purchase is being made?