With sponsorship from Citigroup Inc., Billing Revolution Inc. is trying to help convert people who window-shop on their mobile phones into paying customers.

In December the Seattle vendor plans to roll out a service that will let consumers make purchases with a mobile phone without having to enter their payment card details for every purchase. That step causes many mobile shoppers to abandon transactions they've started.

By simplifying the checkout process, Billing Revolution could encourage more of these consumers to complete purchases. And by tying the service to card accounts that a consumer registers with the service, it provides a way for banks to capture more transaction volume, much in the same way Apple Inc. has with its strategy of routing payments through its iTunes store. Simply put, the card linked to Billing Revolution has the edge over the others in the shopper's wallet.

"It brings … [banks] into the check-in process rather than relegating [them] to the checkout process," said Richard Crone, the chief executive Crone Consulting LLC in San Carlos, Calif.

Billing Revolution, founded in 2007, has caught the attention of Citi, which is providing marketing dollars to sponsor the vendor's Single-Click Checkout service. The service could interest other banks looking to keep their payments cards top of wallet when consumers are shopping, Crone said.

Dickson Chu, the global head of new product development and alliances for Citi's cards business, said Billing Revolution's "ingenious" approach to mobile commerce complements the banking company's technology strategy.

"We're very serious about digital, and within that we're very serious about mobile payments," said Chu, who became familiar with Billing Revolution during a stint at PayPal Inc.

Billing Revolution and Citi are looking at adding additional features for Citi cardholders who use the service, but neither company would be more specific.

Mobile commerce sales are expected to reach $27.3 billion by 2015, up from $1.4 billion in 2009, Aite Group LLC said in a report released last week.

Billing Revolution's service, announced earlier this month, builds on a mobile Web browser checkout service it has been selling to merchants.

Single-Click Checkout is expected to be available for consumer use on Google Inc.'s Android mobile operating system in early December. It would allow a customer to purchase goods and services within a merchant's mobile application without having to key in their card number and other payment information.

"You see merchants that take a look at what they ask for on the Web and they simply replicate that checkout on mobile," Andy Kleitsch, Billing Revolution's chief executive, said in a recent interview. "That [process], we've seen to be a disaster."

Merchants can integrate the Single-Click Checkout service as a payment option into their mobile applications with just four lines of code, Kleitsch said.

The system, which the company eventually plans to make available for app developers on Microsoft Corp.'s Windows Mobile and Apple's iPhone operating systems, also includes a separate app that consumers would download to manage their payment information.

Users would add their card account numbers, mobile phone number and billing information the first time they use it. The information remains encrypted in the program, allowing for one-click purchasing after the account is set up.

The app allows a consumer to add multiple card accounts and will work with debit, credit and prepaid cards.

When consumers proceed to make a purchase within a merchant's shopping app, a window appears on top of the application asking users to click on the card account they want to use.

Consumers who have not downloaded the Single-Click Checkout app on their phones can still use the service but it directs them to a mobile Web page outside of the application. However, the goal is to keep consumers within the app, which typically results in higher transaction rates, Kleitsch said.

Though merchants are already increasing their focus on mobile commerce, the user experience still has room for improvement, Crone said.

"The [user interface] has to be greatly simplified on a mobile browser or inside a mobile application," Crone said. "Merchants and their payment processors haven't had the time or they haven't taken the time to simplify" the interface "for mobile commerce."

Other companies have focused on helping merchants improve the checkout experience for mobile shoppers. At its developer conference in October, PayPal unveiled Mobile Express Checkout, a two-click mobile commerce service.

Zong Inc. and Boku Inc. this summer rolled out software toolkits for developers that want to enable their customers to do single-click checkout in Android apps. These systems send charges to a consumer's mobile phone bill.

Some wireless carriers charge merchants as much as 50% of a transaction cost, though Zong and Boku said for recent agreements they have negotiated fees closer to 10%. Such payments systems, which started out as an alternative for traditional online merchants, focus primarily on the sale of games, ring tones, music and other digital goods.

Billing Revolution, which charges merchants 15 cents or less per transaction, expects merchants of digital goods to be the early adopters of its new service, Kleitsch said. "We think that's going to start to transition as more and more traditional merchants adopt the mobile Web or adopt mobile applications," he said.

Thhat the service is based on payment cards will likely appeal to other banks, though Kleitsch said his company is not pursuing relationships with other issuers at this time.

Neither Billing Revolution nor Citi would say how much the bank paid for its marketing sponsorship. Citi's name is displayed prominently on the developer edition of the app, which Billing Revolution recently released.

A major merchant plans to come out with a new Android app in early December that will include Single-Click Checkout as a payment option, Kleitsch said. (He would not name the merchant.)

While Billing Revolution's service will simplify the checkout process, it faces challenges in attracting consumers, including quelling security concerns that may arise, said Red Gillen, a senior analyst with Celent.

Some consumers may be leery of attaching card accounts to the Single-Click Checkout app, Gillen said.

Kleitsch said a consumer's payment information is not stored on the mobile device or on Billing Revolution's server.

Billing Revolution uses more than 30 attributes tied to a consumer's mobile device to create a unique signature for each customer, he said.

He added that the company recommends consumers set up a password or PIN to protect access to their phone. "We think that's going to become more and more important for people to do that" as mobile commerce grows, Kleitsch said.