Isis has added three new banks to its mobile wallet ahead of its mid-year debut in Salt Lake City and Austin, Texas.

The company, a three-way joint venture formed in late 2010 by AT&T, T-Mobile USA and Verizon Wireless, said today that credit and debit cards from Chase, Capital One and Barclaycard would be included in its smartphone app.

“Mobile commerce is more than a new way to pay; it’s about extending the relationships consumers enjoy with their banks and merchants into a powerful and convenient new form factor,” Isis CEO Michael Abbott said in a statement.

Visa, MasterCard, Discover and American Express agreed last summer to let Isis users load their cards into the mobile wallet app. The service allows consumers pay for goods using smartphones equipped with near-field communication chips.

Isis has not set an official launch date for its mobile payments service. It says it is planning a national rollout after its first two markets light up in mid-2012.

The joint venture gives AT&T, T-Mobile and Verizon a chance to cash in on the burgeoning mobile commerce market.

Isis originally planned to build its own standalone payments network, which would have competed against networks already set up by the likes of Visa and MasterCard. Under its first plan, the company would have collected fees on the payments processed over its network, charging merchants lower rates than existing credit card companies to entice them to sign on for its mobile payments service.

But after a major financial reform bill capped swipe fees, Isis abandoned plans to build its own network in favor of a NFC-based mobile wallet service running on existing payment networks.