Leaving your credit card at the bar may soon be a thing of the past — that is, if you live in San Francisco or New York City. Bloomberg is reporting that Google is planning to trial its new Near Field Communications (NFC) mobile-payment system in both cities. The trial, which could begin in as little as four months, would allow users to make purchases using their smartphones at participating retailers. Presumably, Google will run the trial with the NFC-equipped Nexus S, and it is working with VeriFone to outfit merchants with special cash registers. It’s unclear who will be able to participate in the trial, or which merchants are on board.