The iPhone is a smartphone developed by Apple. The first iPhone was released in June, 2007 and an updated version has been released roughly every year since then. While the iPhone was originally only available to AT&T customers, the iPhone 4 was released on the Verizon network in February, 2010.
The iPhone has a sleek, minimalist design, and differs from other smartphones in its lack of buttons. Most operations on the iPhone are performed using the touch screen display. The only physical buttons include a sleep/wake button, a mute switch, volume up/down buttons, and a home button. All versions of the iPhone have a rear-facing camera, but the iPhone 4 introduced a front-facing camera, which can be used for video calls made using the FaceTime feature. The iPhone 4 also included the first 960 x 640 pixel "retina display," which has double the resolution of previous iPhone displays.
The iPhone 5 and 5s had the same screen resolution as the iPhone 4. The iPhone 6, released in September 2014, provided a larger 4.7" display with 1334x750 pixels. The iPhone 6 Plus, released at the same time, came with an even larger 5.5-inch 1920x1080 pixel display. The iPhone 7 and 7 Plus have the same screen sizes as the 6 and 6 Plus.
Internally, the iPhone runs the iOS, an operating system developed by Apple for portable devices. This allows the iPhone to run "apps," or applications developed specifically for the iPhone. Apps can be downloaded from Apple's App Store, which can be accessed through iTunes or directly from the iPhone's built-in App Store app. There are hundreds of thousands of apps available from the App Store, which provide the iPhone with limitless functionality.