With a new piece of software that allows the iPhone to function as a checkout system, Apple wants to become a direct competitor to companies that sell the digital payment systems used in shops and restaurants globally on smartphones and tablets. With a new payment tool launching first in the US, Apple announced on Tuesday that it plans to allow users to directly accept contactless card payments with any iPhone. In practice, the technology could ultimately see more and more shopkeepers, waiters, bartenders and cashiers whip out an iPhone or iPad whenever someone wants to pay, while undermining …