Mobile wallet joint venture Isis is seeing results from trials in Salt Lake City and Austin, Texas, according to Yankee Group, but research group isn't quite convinced.  

Since the trials were launched in Sept. of 2012, merchants supporting the mobile payment system have seen an uptick in both repeat visits and overall purchases.

 However, Yankee Group analyst Jordan McKeen urges caution, saying skepticism is warranted. 

"It’s no mistake that Isis neglected to provide a sample size for their claims, or failed to offer any insight into the number of wallet activations," McKee wrote in comments. "Until more robust usage figures are provided, it will be necessary to take any of their reports with a grain of salt."

McKee was referring to a report from Mobile Commerce Daily that said users of Isis visit stores five or more times per week on average, and 65 percent of Isis users regularly engage with merchants after leaving their stores. 

That report cited Isis Chief Sales Officer Jim Stapleton, who said the average user of the mobile payments platform follows about five merchants. 

McKee wasn't entirely down on Isis, however. He said that if "Isis’ usage claims do have legs, and its backers have the tenacity to stick it out until NFC gains ubiquitous status, the app will be well positioned for rapid growth.”

The Isis trials are meant to give backers Verizon Wireless, AT&T and T-Mobile USA an indication of whether the mobile wallet could be a source of revenue. 

Isis plans to generate income from promotions and advertisements running on its app, plus fees charged to financial institutions that make their cards available in the mobile wallet. 

The amount of money spent worldwide through NFC mobile payments is expected to grow from $4 billion this year to $191 billion in 2017, according to a recent forecast from ABI Research. The bulk of that growth is expected to come from ticketing and transportation.

The Isis mobile wallet app is currently only available on NFC-capable Android smartphones.