"If this fails, my career is over."

Those words ran through Laura Kelly's head as she helped pitch the Bluebird card to American Express Co.'s (AXP) board of directors. The prepaid card, which resulted from a collaboration between Amex and Wal-Mart Stores Inc. (WMT), proved to be a risk that has paid off handsomely.

Bluebird launched last October. By January, it had over 575,000 account holders and $275 million in funds loaded onto the cards. Eighty-five percent of Bluebird customers are new to Amex, and 45% under 35, according to a February company presentation.

"The entire company got behind that effort ... It was one of the most amazing things I've done in my career," says Kelly, who was Amex's senior vice president and general manager of the Americas. She has since taken a position outside the company.

Watch Kelly's story in her own words in the above video.

Amex has been continuously updating the Bluebird card since its launch. In March, it added FDIC insurance and checkbooks, transforming Bluebird from a prepaid product to a true checking account. Users can now place up to $100,000 into accounts each year.

The new paper checks have an unusual, added security feature. To write a check, a user must first obtain an eight-digit authorization code and set aside funds for the recipient. The payee can then call an 800 number to verify that the funds are available.

"With FDIC insurance coverage, the ability to write checks (even with a pre-authorization requirement) and the increased funding capability, Bluebird has emerged as a very powerful free checking alternative," Jim Marous, a senior vice president of corporate development at digital direct marketing agency New Control, told American Banker in March.

The Bluebird prepaid account was built on top of Amex's Serve digital wallet platform. Amex and Wal-Mart began testing the card in late 2011, and launched the product a week after Wal-Mart put in place a system for reloading prepaid cards at cash registers.

Amex has described Bluebird as an evolving system. It mentioned the check-writing feature at the product's launch, even though it was months away from offering the option.