The iPhone 4 features can be divided up into five headings - Facetime, Retina Display, Multi-tasking, HD Recording and Editing, and a 5MP Camera with LED Flash. These features are what Apple is using to market the latest version of one of their most celebrated products and these features will also be the reason why you want to have an iPhone 4. Let's take a closer and look at what each of these features has to offer.

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Facetime - The iPhone 4 will have a front-facing camera which will make video conferencing finally a reality for the iPhone platform. What's good about the cameras is that you can use both of them for video calling or what Apple calls "Facetime." So, you can either let the person you are talking to see your face or switch to the back camera to let that person see what's around you. While this may seem a welcome improvement to the iPhone 3GS, there is one caveat here - Facetime will only work on an iPhone 4 to iPhone 4 basis.
Retina Display - To put it bluntly, Retina display is Apple's counter to their rivals AMOLED (or Super AMOLED) displays. According to Apple, it's a huge improvement from the iPhone 3GS display capability. It's the sharpest, most vibrant display resolution for the iPhone yet. As such the iPhone 4 will display text in books, web pages, and email crisply no matter what the size is. Of course, it follows that photos and movies will be displayed stunningly as well. Thanks to the iPhone 4 display's high pixel density which is so high that individual pixels are indistinguishable.
Multi-tasking - What can we say? This is one of the most wanted features of the iPhone 4 especially since rival smartphones already offer it. Finally, Apple is bringing multi-tasking to the iPhone 4. With multi-tasking you can switch between running apps without needing to restart each app, receive voice calls while keeping an app open, listen to music, keep GPS running all the time, and of course, complete tasks in the background.
HD Video Recording and Editing - Move over Flip camcorder and the likes, for here comes Apple's take on the handy and mobile video camcorder market. iPhone 4 will let you shoot, edit and share 720p HD video at 30fps. Even more fun is the fact that you don't have to download your video to your Mac anymore for editing purposes. You can edit it right on your iPhone using the upcoming iMovie app for iPhone. Now, this is one feature that will surely make you want the iPhone 4.
5-MP Camera with LED Flash - 5-megapixel may not be that high, especially since some smartphones already offer 8-MP cameras, but hey, it's a big improvement from the Phone 3GS 3.2MP camera, right? And with LED Flash, tap to focus and social sharing features - the iPhone 4's camera is definitely a keeper.