Apple puts it pretty well:
“While everyone else was busy trying to keep up with iPhone, we were busy creating amazing new features that make iPhone more powerful, easier to use, and more indispensable than ever. The result is iPhone 4. The biggest thing to happen to iPhone since iPhone.”

I’ve got to agree! Just look at it and see some of the highlighted features!
FaceTime
People have been dreaming about video calling for decades. And yes, some phones have attempted to deliver video chat, but lets face it, it was shit! iPhone 4 makes it a reality to share a smile from across the globe over Wi-Fi. And it works right out of the box. No other phone makes staying in touch this much fun.
Retina Display
This is plainly the sharpest, most vibrant, highest-resolution phone screen ever, with four times the pixel count of previous iPhone models. In fact, the pixel density is so high that the human eye is unable to distinguish individual pixels. Which makes text amazingly crisp and images stunningly sharp.
Multitasking
Now you can run your favorite third-party apps — and switch between them instantly — without slowing down the performance of the foreground app or draining the battery unnecessarily. No other phones do this!
HD video recording and editing
You can shoot your own movies in high definition. Let me repeat that: You can shoot your own movies in high definition! Even in low-light settings, thanks to a backside illumination sensor and built-in LED light. Then edit and create your own mini-masterpiece right on iPhone 4 using the new iMovie app that has themes, titles, and transitions.
5-Megapixel Camera with LED Flash
The new 5-megapixel camera has a built-in LED flash. The advanced backside illumination sensor captures great pictures even in low light. And the new front-facing camera makes it easy to take self-portraits. Bang!
And you can get a variety of skins to dress it up too:

While you’re here, go see an iPod Shuffle covered in sweet chocolate.
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