iPhone 4

Antennagate was a hardware flaw where holding the lower-left corner of the stainless steel phone bridged two external antennas, causing cellular signal loss. Apple eventually offered free bumper cases to mitigate the issue and held a rare press conference to address the backlash. It became one of the biggest PR challenges of Steve Jobs' tenure.

Apple introduced the 'Retina Display' with the iPhone 4, which boasted a resolution of 960x640 pixels at 326 pixels per inch (PPI). This was the first screen on a smartphone where individual pixels could not be discerned by the naked eye at normal viewing distances. It set a new industry standard for mobile display clarity.

The iPhone 4 introduced Apple's FaceTime video calling platform, which originally only worked over Wi-Fi between two iPhone 4 devices. The 0.3-megapixel VGA camera also allowed users to take early 'selfie' photos. It fundamentally changed the way people used smartphones for personal communication.

The iPhone 4 shipped with iOS 4, which introduced major features like multitasking for third-party apps and folders for organizing the home screen. It was the first version of the operating system to officially bear the 'iOS' name, having previously been known as iPhone OS.