Computerworld - American Express Thursday announced the national rollout of mobile payment system that pairs its Amex credit card with a user's smartphone-based Foursquare profile to offer discounts for retail purchases. The discounts, initially available from retailers H&M and Sports Authority, are credited to a user's Amex card within three to five days of a purchase, the company said, adding that no coupons, smartphone codes or NFC smartphone chips are needed. Foursquare, a mobile platform that uses GPS technology, currently has more than 10 million subscribers who use the service as a social network to share their location with friends. The joint effort requires that cardholders register with Amex to link their card to their Foursquare profile.