Walmart may be working on a self-pay checkout system that uses the Apple iPhone, says a report in Reuters. A survey on Survey Monkey suggests Walmart employees are testing the system at a store in Rogers, Ark. In this self-pay system, customers would scan items with their iPhones while they shop. When they are done shopping, the customer would pay at a self-checkout counter. The checkout system would reduce costs for retailer and shorten checkout times for customers.