US retail giant Walmart said it was testing a checkout system in which customers use their phones to scan items and then pay at self-serve kiosks. The motivation behind the new system, Walmart said, is the $12 million per second that the company pays cashiers, The Wall Street Journal reported Saturday. The company already said in March that it would add self-checkout lanes to many stores to cut back on lines and reduce its labor costs. The mobile check out system is being tested in one Walmart super center store near its headquarters in Bentonville, Ark. It is not being tested by the public, but by Walmart employees, the Journal said.