has launched an iPhone application that gives shoppers easy access to online coupon codes when shopping via iPhone and the ability to compare in store prices with online discounts when out at the mall. With over 50,000 coupons from 10,000 merchants, RetailMeNot is one of the largest online coupon Web sites on the Internet. A recent study of nearly 4,000 shoppers who stopped at to pick up a coupon before making a purchase saved an average of US$29 on an average purchase of $151.