Apple CEO Steve Jobs says the iPhone 4, which debuted on Monday, is the “biggest leap forward” the iPhone has made since it was introduced in 2007.

The newly announced phone has “one of the most beautiful designs you’ve ever seen,” Jobs said at a tech conference in San Francisco. “This is without a doubt the most precise thing and one of the most beautiful things we’ve ever made.”

Here’s a quick list of 10 things you should know about the iPhone 4, which goes on sale June 24, and costs between $199 and $299. Let us know if you have more questions and feel free to leave thoughts of your own in the comments section at the bottom of this story.

Sharper screen

In his Monday keynote address at Apple’s Worldwide Developers Conference, Jobs sounded more excited about the iPhone 4’s new screen than anything else.

With 326 pixels per inch — four times that of previous Apple phones — Jobs says the iPhone 4’s “retina display” screen is years ahead of anything else on the market.

“Text looks like you’ve seen it in a fine printed book — unlike you’ve ever seen on an electronic display before,” he said. “Once you’ve used a retina display you can’t go back.”

Gyroscope

“These phones are getting more and more intelligent about the world around them,” Jobs said. That’s true of the iPhone 4, which has five sensors, including a gyroscope.

What does that mean for users? Probably cooler games and apps. The iPhone 4’s internal gyroscope can sense motion on six axes. On Monday, Jobs showed a demo where he pivoted in a circle, and the stack of blocks in an app spun with him. The phone is basically more aware of where it is in the world, in relation to gravity, than it was before. It’s hard to say exactly what app developers will do with this, but likely something.

Thickness

The iPhone 4 will be the thinnest smartphone on the market, Jobs says. At 9.3 millimeters (0.37 inches) thick, it is 24 percent thinner than the previous iPhone model, the 3GS, he said.

“I don’t think there’s another consumer product like this,” he said. “When you hold it in your hand it’s unbelievable.” The iPhone 4’s screen remains the same size as before, 3.5 inches when measured diagonally. That makes it smaller than some Android phones, which are its main competitors. But that may not be a good thing. As people watch more video on their phones, they’re demanding larger screens, some analysts say.

Camera flash

In what’s largely seen as a catch-up move, Apple added an LED flash to the iPhone 4’s camera, which lets mobile photographers shoot photos and video more easily at night.

Better camera

The quality of the iPhone 4’s camera is improved over previous models. The iPhone 4 shoots photos with 5 megapixels of resolution, compared to 3 megapixels before. That’s still not the best on the market. The HTC Droid Incredible has an 8-megapixel camera, for example. The Nexus One, another competitor, has a 5-megapixel camera, too.

The iPhone 4 also shoots HD video, and a video-editing app called iMovie, which Apple will sell, allows people to shoot, edit and share videos with the phone.

Video conferencing

In addition to the back-of-the-phone camera improvements, Apple also added a second camera to the iPhone 4, which faces its user. This can be used for video conferencing, which Apple and Jobs expect to be an emerging trend in mobile phone use. For more on this.

Multitasking

The iPhone’s operating system, which Apple calls iOS 4, got an upgrade along with the iPhone 4’s hardware. Among the most-awaited changes is multitasking, which means that the phone can run multiple applications at once. Want to listen to internet radio and check e-mail at the same time? Starting on June 21, you can with the iPhone.

Several other smartphones have featured multitasking for some time. So Apple is not blazing new territory here. Jobs says the company waited to add the feature until it could do so without sucking down too much of the phone’s battery life.

Stainless steel antennae

The iPhone 4 is flat on the front and back, and a band of stainless steel goes around the edge as a trim. This isn’t just a design feature, Jobs said. It’s actually the antennae.

“It’s never been done before and it’s really cool engineering,” Jobs said.

Guts

The iPhone 4 has a new processor — the A4 — which Apple says makes the phone faster than competitors and faster than the processor in the iPhone 3GS. Apple debuted the A4 processor as part of the iPad slate computer in January.

But the iPhone 4’s capacity to store books, videos and music disappointed some. The high-end model stores 32 gigabytes of data, which isn’t any more than the iPhone 3GS.

Wireless carrier

The iPhone 4 is only available with a contract from the wireless carrier AT&T. That’s bad news for some people. Bloggers have been begging Apple to open the iPhone to multiple carriers — and specifically to Verizon — for some time. Some iPhone users, particularly those in bigger cities like New York and San Francisco, have complained that AT&T drops their calls and doesn’t handle data requests quickly enough.

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