IPhone 4

 The iPhone 4 is a model of smartphone that was released by Apple in June 2010, superseding the iPhone 3GS.

Background
Like previous models of iPhones, its key features included a native mailing app, a web browser, SMS messages, a phone function, and an iPod player, among other things. The iPhone 4 originally shipped with iOS 4 and could be upgraded up to iOS 7.1.2.

It first came in in 16 and 32 GB versions, only in black. On February 7, 2011, Verizon released a CDMA iPhone 4, ending Apple's exclusivity agreemnent with AT&T. A lower cost 8 GB model and white version became available later, unlocked from Apple's website.

Features
iPhone 4 features a new 5 megapixel camera with four element lenses, improved white balance and tap to focus for video. a front 0.3 megapixel camera for FaceTime is included. HD 720p video is included. Retina display gives 4x more pixels than previous generation, 326 ppi at 960x640.

Cameras
The iPhone 4 is the first iPhone model to have dual cameras. The front features a 0.3 megapixel selfie camera. The back has an upgraded 5 megapixel camera with an LED flash and can now record in HD 720p video.

FaceTime
The iPhone 4 adds a new feature to the iPhone line, FaceTime. FaceTime allows a user to make a video call over Wi-Fi connection to another iPhone 4 (or up), iPod Touch 4 (or up), a Mac running 10.6.7 or later, or an IPad 2 or later.

Retina display
The display on the iPhone 4 is designed by Apple and manufactured by LG. It features a multi-touchscreen with pixel density of 326 pixels per inch (ppi)and res. of 960x640. The screen is marketed as a "Retina display", based that 300 ppi at 12 inches from the eye is the maximum amount of detail the human retina can distinguish.

"Death grip"
Users experienced what appeared to be a dramatic drop in signal bars when gripping the iPhone 4 across antenna seams on the sides of early iPhone 4 models. Apple engineers discovered that this caused was by the formula that calculated signal strength. This discovery, combined with Steve Jobs' initial reaction in blaming users for how they were holding their phones, was dubbed by the media as "Antennagate".

On July 16, 2010, Steve Jobs held a press conference at the Town Hall at the Apple Campus in Cupertino to announce that the company would provide a free case to all iPhone 4 customers to improve signal bars. He also toured the press through Apple's once-secret wireless lab to show how iPhone models were tested. The version of the iPhone 4 that was introduced in February 2011 through  repositioned the antenna seams to minimize the "death grip" effect. The signal bar display problem was supposedly addressed with the release of iOS 4.2.

Bumper
An iPhone 4 Bumper is a ring of rubber that covers the edges around the iPhone 4. The Bumper is designed to protect the iPhone 4, but has the added effect of insulating the antenna on the sides from contact with the user's hand. A different design was introduced to fit the version of the iPhone 4 which repositioned the antenna seams. This antenna configuration was carried over into the iPhone 4S.

Carriers
The iPhone 4 was originally released exclusively to AT&T in the U.S. On January 11, 2011, Verizon announced that they would be selling a CDMA version of the iPhone 4 the following month. They added a 'Mobile Hotspot' feature allowing users to use the iPhone as a wireless hotspot for up to 5 connected devices. They also incorporated a new antenna design which was said to avoid the "death grip" problem.

Hardware

 * Samsung S5L8920 Application Processor → Apple A4 System-On-Chip
 * ARM Cortex-A8 32-Bit Core Processor
 * ARMv7 and THUMB-2 Instruction Set
 * 1Ghz (underclocked to 600Mhz to prevent overheating) → 1Ghz (underclocked to 800Mhz to prevent overheating)
 * 256MB SDRAM → 512MB SDRAM
 * Integrated PowerVR SGX535 Graphics Card
 * Toshiba TH58G6D1DT (NAND Flash Storage)
 * Marvell 88W8686 (Wi-Fi)
 * Broadcom BCM4325 (Bluetooth)
 * Infineon X-Gold-608 → Infineon X-Gold-618 (GSM), Qualcomm MDM6600 (CDMA) (Phone, Messages, and Cellular Data)
 * Infineon Hammmerhead II PMB2525 → Broadcom BCM4750 (GSM), Qualcomm MDM6600 (CDMA) (GPS)