Paying for something from a mobile phone still isn't an option in most U.S. brick-and-mortar stores. But that reality is obscured in San Francisco. The Bay Area has been an early testing ground for a future full of smartphone-based transactions, with all sorts of companies, from Starbucks and PayPal to Google and startups like LevelUp getting involved [see "Battle of the Electronic Wallets"].

Into this crowded field comes GoPago, a startup that began widely marketing its own payment app in San Francisco this April after expanding from a smaller pilot program in the region.

The 70-person company has built a network of about 300 active merchants in the city so far, but it is a startup worth watching for another reason—one of its investors and strategic partners, as of February, is JPMorgan Chase, one of the nation's largest banks and card issuers.

"This is a very, very competitive area. We're still in the very early days of what could be a revolution in how people pay for things," says Jack Stephenson, a former PayPal executive who is now JPMorgan Chase's managing director for mobile, payments, and e-commerce.