They'll launch, make a couple hundred mil, then they'll get hit with fraud, a ton of people will lose money, and they'll be forced to shut down, since noone will want to use the service, in fear of getting defrauded.
Since there is no barrier to entry, it'll be like 2 weeks before someone comes out with a black market version, that will look exactly the same, but instead of processing credit cards, it'll store them for future fraud.
Will be like the ATM snooping devices, but instead of having to get into the bank, all you need is an iPhone, and some "small" business to rob people with. A taxi, or a newspaper stand.
Edit: If you are going to downvote, at least tell me how exactly do you think this will avoid fraud from fakers who imitate the look and feel of the device?