Imagine being able to use your mobile phone to pay taxi and mass transit fare; use vending machines; make retail purchases; and check in at hotels. Every day, millions of citizens in Japan, S. Korea, and soon Singapore do so simply by waving their mobile phones in front of point-of-sale terminals using near-field communication or related technology. But, while the technology is readily available in the US, it will be some time before Americans can use their cellphones as mobile wallets.