Want to leave your wallet behind and swipe your mobile phone instead? Technology enabling portable devices to function as debit or credit cards has arrived, but adoption has been slowed by companies wrangling to control user fees. "The stakes are enormous because small, hidden fees that are generated every time consumers swipe their cards add up to tens of billions of dollars annually in the United States alone. 'It all comes down to who gets paid and who makes money,' said Drew Sievers, chief executive of mFoundry, which makes mobile payment software for merchants and banks."