Is there a mobile payment system that can be combined with foursquare?
Answer by Aaron Greenspan:
Foursquare could presumably integrate with any payment system it wanted to. PayPal has had APIs available for years; Authorize.Net has facilitated online transactions via credit card for a decade, Venmo has a peer-to-peer system that's receiving a lot of hype, etc. The real question is whether or not it would do any good without additional POS integration to keep track of transaction data.
POS integration is difficult and expensive, and it's something we're working on quite seriously as part of our efforts with FaceCash. It's true that Foursquare could integrate with FaceCash just as it could with anyone else, but the way we see it, why bother "checking in" at all when you could simply note (publicly if desired) that you just paid for something? In that case, the payment system suddenly makes the value of check-in services questionable in the first place.