In a move intended to stimulate the market, Isis says it is taking its mobile payment scheme nationwide … sometime later this year.

The mobile wallet joint venture — formed by AT&T, Verizon Wireless and T-Mobile USA — has been testing its payment technology in Salt Lake City and Austin since October.

The cities have been a petri dish for the consortium, explains Jaymee Johnson, Isis' head of marketing.

He says that since last fall, the number of merchants with contactless touch pads (the key ingredient for smartphone-aided payments) has quadrupled to roughly 4,000 locations. Those users are tapping their phones, on average, roughly 10 times a month.

Isis is, however being coy about setting an actual country-wide launch date.

"We are just saying that we are launching this year, simply to give the broader ecosystem time to act," he says, in an interview with American Banker. "It's important for us to give the market visibility into where we are going and what we are doing."

By announcing a timeline of the rollout, Isis is hoping to stimulate banks to sign up for the service and merchants to invest in payment terminals.

The technology — which relies on small, removable plastic SIM cards to hold payment credentials — works only with near-field-communication enabled phones. NFC allows a person to tap and go at the point of sale.

Carriers will update their customers' SIM cards through upgrades, new contracts, or requests.

Today, Isis says, 35 devices from AT&T Mobility, T-Mobile and Verizon Wireless currently support Isis' method.

Some of the most popular smartphones — namely the iPhone (a nod toward a possible NFC-enabled version), Windows Phone and Blackberry 10 — are expected to support Isis later this year, Isis says.

Banks and merchants who want to offer loyalty rewards using Isis' payment technology must sign up with the joint venture. Already, JPMorgan Chase, Capital One and American Express have done so.

Consumers can also fund mobile payments with a prepaid Isis Cash card.

However, onlookers remain dubious of the joint venture's value.

"My firm has three very large national retailers in the U.S. and two in Latin America as clients. Although Isis' value proposition of connecting mobile devices with a retailer's physical environment is extremely interesting to our clients, Isis is not top of mind as it remains unclear what its advantages are," says Philip J. Philliou, a payments consultant, in an email. "I understood Isis when they planned to compete with Visa and MasterCard. I am not sure what they stand for now. I need to hear something meaningful."

Indeed, the joint venture has been difficult for many to figure out.

"Is it fizzle or will it sizzle?" says Brian Riley, a senior research director in the bank cards practice at CEB TowerGroup. "They really haven't solved the issue of replacing this infrastructure. It's not cheap. So are you just going to create another monster that processes at one-and-a-half percent?"

Regardless, Isis hopes to drive adoption.

"We consider this just the start," says Johnson of the rollout. "This isn't the destination, it's just the start. These are really the early days of mobile commerce in general."