NEW YORK » Apple is expected to reveal a digital radio service and changes to the software behind iPhones and iPads today as the company opens its annual conference for software developers.

Apple hasn’t said what it will unveil at the Worldwide Developers Conference in San Francisco. But the major announcements are expected during today’s keynote presentation. Last year, Apple used the conference to announce its own mapping service, better integration with social networks and improvements to virtual assistant Siri. It also announced thinner MacBooks with high-resolution screens. The conference runs through Friday.

This year, Apple is expected to show off a simplified look on iPhones and iPads. If the speculation is correct, it would be the most radical design change since the iPhone made its debut in 2007, showing consumers that phones could do much more than make calls and exchange messages.

This week’s event comes at an important time for Apple. The company’s stock price has fallen amid concerns that another breakthrough product isn’t imminent. Although CEO Tim Cook has said people shouldn’t expect new products until the fall, Apple is likely to preview how future products will function in its unveiling of new services and features.

Today’s highlight is expected to be an updated version of iOS, the software that runs iPhones, iPads and iPod Touches. It will be called iOS 7 and will come with new devices expected to go on sale this fall. Owners of recent models such as last fall’s iPhone 5 will likely be eligible for free upgrades.

Icons in iOS now have a three-dimensional look that tries to mimic the real-world counterparts of certain apps. For instance, the icon for the Notes app looks like a yellow notepad and the Contacts app is represented by a leather-bound address book. The speculation is that Apple will do away with that theme in iOS 7. Instead, icons will look plain and simple, offering more consistency from app to app. The new design is likely to favor black and white elements rather than splashes of color.

While design modifications could help Apple distinguish its devices from rival phones and tablets, they risk alienating longtime users.

Microsoft’s radical makeover of the Windows operating system in October was meant to give the company a stronger presence on tablet computers, but it ended up confusing many people who had become accustomed to using the old operating system on traditional desktops and laptops. IDC blamed Windows 8 for accelerating a decline in PC sales.

Apple riled users of its gadgets last fall when it kicked out a beloved app using Google’s mapping service and replaced it with its own Maps app. Travelers complained of misplaced landmarks, overlooked towns and other problems. What was supposed to be a triumph for Apple served to underscore Google’s strength in maps. Apple CEO Tim Cook issued a rare public apology and promised improvements.

Apple may use iOS 7 as an opportunity to update its Maps app. Other features in iOS 7 may include new ways to do things through gesture commands.

Apple is also expected to debut a streaming music service dubbed iRadio.

Apple is a pioneer in digital music sales. The debut of its iTunes music store in 2003 gave people an easy, legal way to obtain music for their iPods. Apple persuaded the major recording companies to join its efforts as a way to thwart online piracy. What started with a catalog of about 200,000 songs has grown to tens of millions today. The iTunes store is now the leading U.S. retailer of music.

With iTunes, people buy songs or albums to download to computers, phones and tablets. But streaming services such as Pandora and Spotify have emerged as popular alternatives for listening to music. Pandora relies on its users being connected to the Internet at all times and plays songs at random within certain genres for free. The service is supported by advertising. It is the most similar service to the one Apple is expected to announce today The difference is that Apple is expected to feature a seamless way for listeners to purchase songs through iTunes.

The announcement could further cement Apple as a leader in digital music and cut into Pandora’s status as the most-listened-to Internet radio service.

But Apple faces a new type of competition that it didn’t have when it debuted iTunes. Rival Google Inc. started an on-demand subscription music service called All Access last month. The service joins Spotify, Rhapsody and others that give subscribers the ability to pick and choose specific songs and albums from a catalog of millions for playback on computers, tablets and smartphones. Such services allow songs to be saved on mobile devices for playback outside of Internet connectivity as long as the user keeps paying a monthly fee — usually $10 a month in the U.S.

Apple Inc. faces more competition on phones, too. Phones running Google Inc.’s Android system have surpassed iPhones in sales. In addition, new phones running Microsoft Corp.’s Windows Phone 8 system and Research In Motion Ltd.’s BlackBerry 10 have started going on sale in recent months.

AP Business Writer Ryan Nakashima in Los Angeles contributed to this story.