The mobile payments venture Isis has already signed some major banking companies to its smartphone-based payment system. Its newly announced merchant roster likewise features big-name participants.

Aeropostale, Coca-Cola, Champs Sports, Dillard's, Foot Locker, Jamba Juice, and Macy's are among the national companies that have signed on with Isis during its trials in Salt Lake City and Austin.

Every new payment system faces the problem of appealing to multiple participants at once. Isis, which was launched by Verizon Wireless (VZ), AT&T (NYSE:T) and T-Mobile, initially had only Barclays signed on as an issuer. It has since added JPMorgan Chase (JPM), Capital One (COF) and American Express (AXP).

It has, until now, been less vocal about merchant participation.

"What this is really about for [our users] is answering a very relevant question for them," says Jim Stapleton, Isis' chief sales officer. After learning how to download the Isis app and load funds, the next big question for consumers is where to use it, he says.