The original iPhone unveiled by Steve Jobs in 2007 had a 3.5-inch screen.
Jobs introduced the first iPhone at the Macworld Conference & Expo in San Francisco on January 9, 2007. The device combined a mobile phone, a widescreen iPod, and an Internet communications device, and it used a 3.5-inch multi-touch display instead of a physical keyboard.
The original screen had a 320-by-480-pixel resolution and a 3:2 aspect ratio. This design became a recognizable feature of early iPhones before Apple moved to larger displays with later generations.
A frequent mix-up is remembering the screen sizes of later models. The iPhone 5 increased the display to 4 inches, while several later iPhone families introduced 4.7-inch and larger screens. Those specifications do not apply to the first-generation model.