The number of NFC (near-field communication) transactions with Google Wallet doubled in the first six weeks after the Aug. 1 of a cloud-based version, and that trend has continued, said Osama Bedier, Google's vice president of wallet and payments, in a session at the Global Mobile Internet Conference in San Jose, California. He didn't say how many payments that is, however. Google has never quoted an exact number of transactions, and Bedier stuck to that practice.

"We feel like we're making a huge difference on transaction volume," Bedier said in an on-stage conversation with Rajeev Chand of investment bank Rutberg & Co.

However, mobile payments won't be an overnight success, he said. "We didn't think NFC was just going to happen in a single year. This is a three-to-five-year game," Bedier said.

U.S. consumers have shown limited interest in mobile payments because the country has a well-developed credit-card ecosystem, analysts say. Payments with NFC require hardware and software in both handsets and point-of-sale terminals. In addition, there are three systems competing, each with a different set of strong backers.

In addition to Google's NFC payment technology, part of its overarching Google Wallet program for virtual wallets, there are systems being promoted by big mobile operators and by retailers. The ISIS consortium, which includes AT&T, Verizon Wireless and T-Mobile USA, plans to launch its platform in two cities on Monday. In August, a group of stores including Walmart, Target and 7-Eleven formed their own , Merchant Customer Exchange.