Stephen Shankland/CNET

It's not every day that a new mobile operating system arrives, but Tuesday will be one of them as Telefonica begins selling the inexpensive ZTE Open with Mozilla's Firefox OS in Spain.

The move marks the commercial beginning of an effort by phone makers and network operators to use Mozilla's open-source, browser-based operating system to reclaim power in the mobile market lost to Apple and Google.

The phone itself costs 69 euros ($90), including 30 euros ($39) of pay-as-you-go credit -- or for those who sign up for a two-year contract, for 2.38 euros ($3.10) per month. That's a lot cheaper than most of the new Android and iOS smartphones on the market today that consumers have flocked to and that Firefox OS is competing with.

The ZTE Open won't impress smartphone power users who want more than its 3.5-inch 480x320-pixel touchscreen, 3.2MP camera, 256MB RAM, and 512MB flash memory that's boosted with an included 4GB microSD card. But it's not designed to win them over; it's more for new and cost-conscious smartphone buyers, Yotam Benami, Telefonica's digital director of open Web devices, said in an interview.

So why would a customer buy it? "We're excited about dynamic app search," which finds apps and pages on the Web rather than on app stores. "It's a very personalized experience. You can interact with Web apps in the cloud." He added, "The entire user experience is more simple and streamlined. Many users are frustrated with the complexities of Android," and low cost and long battery life are compelling advantages especially in emerging markets.

This single Firefox OS phone in a single market soon won't be alone. Telefonica also will sell another lower-end phone, the Alcatel One Touch Fire, and will launch the phones in Brazil, Venezuela, and Colombia, Benami said.

Telefonica is not the only carrier on board. Telenor will launch its first Firefox OS phones in central and eastern Europe later this year, and Deutsche Telekom will do so in Poland. There are also several other Firefox OS supporters, including original equipment manufacturers (OEMs) such as Sony and LG Electronics that build handsets -- and a sizeable list of carriers.

For many of these allies, Firefox OS provides a way to loosen the mobile marketplace control of Apple and Google, which control not only their operating systems but also the app stores used to distribute software.

"The current dynamics of the mobile ecosystem are problematic for OEMs, for developers, for end users, and for carriers," Benami said. "Firefox resolves many of these issues."

Developers get multiple pathways to market, he said. Handset makers get new choices and "a path to lower level of litigation," a reference to the swarm of mobile-market lawsuits between the biggest mobile players. And for carriers, "we are not bound by rules set by one particular company that owns the platform."

As the difficulties at Microsoft and BlackBerry have shown, it's hard to compete against Android and iOS. The Firefox OS supporters think they have a recipe that will work, though, in part because of the billions of people who haven't yet entered the market and because the operating system uses Web programming that means the developer and app ecosystem isn't starting from scratch.

It's that Web connection that gives Firefox OS its edge over other mobile OS challengers, said Mozilla Chief Operating Officer Jay Sullivan.

"The only remaining ecosystem is going to be around the Web," Sullivan said.

Even though Web pages and Web apps work on Firefox OS devices, there's still a lot of programming work to be done. Challenges include support for multi-touch interfaces, learning how to write Web apps that use new interfaces like accelerometers and offline support, and the much broader issue of adapting pages to small screens and slow mobile networks.

For that reason, Mozilla is fleshing out developer documentation and holding evangelism and training events around the world for programmers. And it's promoting the Geeksphone Keon for developers.

Plenty of developers will need a presence on the Web, and they'll be able to reach Firefox OS users, Sullivan argued.

"When you look at the long tail of highly relevant local apps, a lot of people developing those are small local developers," he said. "They don't have the money to develop an iOS app, an Android app, and a Web app."