New York-based Isis today will  unveil alliances with American Express (AXP), Discover (DFS), Master Card (MA) and Visa (V) — the major companies that settle payments among banks, consumers, merchants and other parties — at Fortune’s Brainstorm Tech summit in Aspen, Colo.

Isis aims to install its software on a new generation of mobile handsets that, in turn, exchange information with special terminals at retailers, restaurants and other outlets.

But rather than settling those transactions itself or billing customers’ phone statements, Isis believes working with the payments networks will make mobile payments more appealing to consumers and merchants, who can continue to use or accept the card platforms of their choice — only instead of using physical cards the parties will swap digital information wirelessly.

“This is a major milestone,” says Isis CEO Michael Abbott.”We’re bringing together incredibly fierce competitors for the common good of helping consumers make mobile payments.”

He says all four payments networks will participate in the company’s initial launches in Salt Lake City, Utah, and Austin, Texas, in early 2012.

Isis competes with other mobile-payments platforms including Google’s (GOOG) Google Wallet and  Ebay’s (EBAY) PayPal Mobile service — and even mobile platforms that companies such as Visa are developing themselves.

But Abbott says the simultaneous endorsement of the four credit-card networks suggests that Isis has convinced a bit part of the payments world that it is a good partner. “We’ve got a very good model that’s great for the industry,” he says.

To be sure, Isis and its peers face many hurdles before consumers, banks and merchants adopt mobile money en masse. Today very few “cash registers” are set up to accept a phone instead of a credit card, and similarly only one widely available phone in the U.S., Google’s Nexus S, is tricked out with the necessary chip for so-called Near Field Communications that the industry hopes to adopt as the standard for transferring data from phones to in-store terminals.

But perhaps the biggest hurdle is convincing consumers that a “bump” with their phone is somehow superior to a simple swipe of a credit card.  And, as the New York Times recently noted, using one’s cellphone as a wallet assumes that the cell phone is, in fact, charged and ready to go. If it runs out of juice, Google e-commerce executive Stephanie Tilenius told the Times,  “I think you need to use your plastic at that point.”