As smart phones increasingly appear alike, with high-end models mostly taking their cues from Apple Inc.'s iPhone, more and more it's the software they run that makes a difference.

A growing number of operating systems are jostling for the attention of phone buyers and manufacturers. The winners will determine what our phones can do, which Web sites we're steered to, and which manufacturers will survive the next few years.

The battle will be on display as wireless carriers and phone makers gather this week in Spain for the industry's largest trade show, Mobile World Congress.

Analysts don't expect smart phones to settle on one kind of operating software, like the PC industry largely has with Microsoft's Windows. But analysts do expect the smart phone field to be winnowed down to two to four winners over the next few years.

These are the contenders, starting with the largest worldwide market share:

• Symbian — Nokia's use of Symbian software has taken it to the top, but its perch is precarious. It's down from 56 percent worldwide share in 2008 to 44 percent in 2009, according to research firm In-Stat. Even though it's No. 1 in the world, it's nearly unknown in the U.S. One problem is that Nokia and Symbian have failed to keep up with the latest trends in the U.S. market, particularly touch screens.

• iPhone — Apple's phone continues to roil the industry, and its sales more than quadrupled last year. Its features are a model for competitors, and it has by far the most support from application developers, despite complaints about the company's opaque and slow approval process.

But while Apple is likely to be one of the winners in the smart phone fight of the coming years, its reach will be limited because Apple doesn't allow any other manufacturer to use the iPhone operating system.

• BlackBerry — Research in Motion Ltd. of Canada uses its own software for its BlackBerrys and doesn't license it to others. Though sales are growing strongly, they could not keep up with Apple's growth last year, and the iPhone's market share at 19.8 percent edged past the BlackBerry's 19.2 percent, according to In-Stat.

RIM has a nearly impenetrable hold on the market for corporate e-mail phones in North America, so analysts expect it to stay around. However, it has stumbled in trying to expand to the consumer market and in introducing touch screens.

• Windows Mobile — Once a pioneer in smart phones, Microsoft is struggling to keep up. Firms like Motorola Corp. and HTC Corp. are shifting away from Windows Mobile toward Google's Android. Last year, fewer Windows Mobile phones were sold than the year before, even in a market that grew 35 percent.

Microsoft is expected to show off a new version of its mobile software Monday in Barcelona. Analysts see that as a do-or-die attempt to stay relevant in the business.

• Android — Google's software has been on a tear, racking up a lot of support from manufacturers, and favorable reviews. There was just one Android phone out in 2008. At the end of 2009, there were more than a dozen, from Motorola, HTC and Samsung and others.

Android is free for manufacturers as part of Google's effort to stimulate use of its Web services on cell phones. It's attracting a lot of attention from application developers, but the offerings still don't match those on the iPhone, either in quantity or quality.

• webOS — Palm Inc. more or less created the smart phone then limped along for years with aging software that had its roots in the Palm Pilots of the mid-'90s. Last year, it made a clean break, introducing the new webOS, running on two phones, the Pre and Pixi. It's the only phone software that does a good job of running several applications at once and letting the user switch between them. It's gotten good reviews, but sales have been less than stellar. In the U.S., the phones were exclusive to Sprint Nextel Corp. until January, when Verizon added two new models. AT&T Inc. plans to add webOS phones later this year.

• LiMo — Short for Linux Mobile, LiMo is a consortium that gives away its software. Its selling point is that it gives wireless carriers and manufacturers the freedom to put their own stamp on their cell phones. It's also suitable for cheaper, non-smart phones. But uptake has been minimal, and Android and the free version of Symbian seem to have stolen a lot of LiMo's thunder. Motorola uses LiMo for some nonsmart phones, but is now focusing on Android. Carriers may like the idea of customizing their phones, but consumers are more focused on phone brands that stretch across carriers, like the BlackBerry.