Editors' note: This slideshow has been updated with four new slides. The original publish date was April 9, 2010.
Multitasking is the biggest win from iOS 4. It's great to have this common smartphone feature, though we're disappointed it will come only to the iPhone 3GS (or later) and not the iPhone 3G.
To access the multitasking menu, double tap the Home button. You'll see a list of currently running applications that you can scroll through using a sideways finger swipe. You then open an application by tapping its icon.
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More mulitasking
To close a running application, first use a long press on the related icon. You'll then see a tiny delete icon in the top left corner.
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Easy access to controls
Double-tap the home button to bring up the multitasking screen and scroll one screen to the left to access iPod controls. You also can lock the screen rotation from this screen or return to iTunes with a touch of your finger.
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Home screen folders
We also welcome the new ability to add home screen folders. To create a folder, just drag icons on top of each other. The folder will then appear as a square with tiny icons of the included app inside. Tap the the folder to open it.
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Naming folders
You can change the default folder name if you wish. To remove apps from a folder, just drag the related icon back to the home screen.
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Unified in-box
We've long asked for a unified e-mail in-box, and now we have it. Alternatively, you can select in-boxes for individual accounts.
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Threaded e-mail search, step one
iOS 4 adds the ability to see e-mails by thread. To get started, select the gray double arrows next to a message.
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Threaded e-mail search, step two
You'll now see only those e-mails in the selected thread.
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Delete e-mails in search
When searching your e-mails, you can delete messages directly from the search results.
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Home screen backgrounds
The new OS lets you change the home screen background. The only trouble is you can't get back to the standard black background once you remove it.
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Home or lock screen?
When selecting a wallpaper, you can use it as the home screen background, the lock screen background, or both.
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Camera zoom
In the still camera you get a 5x digital zoom. Tap the display to access the feature.
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Rotate photo
In the photo gallery menu you can choose to rotate an image 90 degrees.
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Image sorting
Find all the images that have a specific friend in them using the Faces sorting feature. You'll need to have already used the face recognition options in iPhoto or Aperture and synced with iTunes to use this feature.
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Geolocation of photos
The addition of Geolocations lets you view where you took your latest shots on a map and sort your images by location.
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Location Services menu
A new Location Services menu lets you decide which programs can use your location information and which ones can't.
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Spell check
Though the iPhone has long had an autocorrect feature, the new spell check feature will notify you of unrecognized or misspelled words with a red underline.
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Web search suggestions
When typing a search term in the Safari browser you'll get Google suggestions along with your recent searches.
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Text message search
You can search text messages just as you've always been able to search your e-mail in-box.
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Universal search
When using the universal search feature you can access the Web and Wikipedia results for your search term.
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Playlists
In the iPod player, Apple added new playlist creation options.
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Birthday calendar
If you can't remember birthdays, you'll like the birthday calendar.
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Game Center
The Game Center lets you connect with and challenge friends online. Create an account and enter custom text that will be seen by your friends.
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That's all, folks
Welcome to iOS 4!
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