Smartphones have grown larger over the years, making them harder to use with one hand, especially when trying to reach controls on the screen. The iPhone Duo is a proposed design that offers a potential solution to this challenge. As manufacturers have made screens longer and thinner, certain areas have become difficult to reach, particularly for users who hold their phones with one hand. The iPhone Duo addresses this by placing the dock and main controls on the right side of its external screen, bringing them closer to the thumb. This design places the thumb at the center of the screen, which is considered one of the most innovative aspects of the imagined format. When the iPhone Duo is closed, its external screen does not simply display the usual iOS interface seen on a traditional iPhone. Instead, the interface is adapted to the unique shape of the device, with a wide display area on the left and the main navigation elements grouped on the right. This setup allows users to view content on a large screen without having to stretch their fingers to reach the controls. The problem of reachability on modern smartphones is well known, as screens have become longer over time. Smaller smartphones allowed easier access to different areas of the screen with one hand, but they came with the trade-off of a smaller display area. The iPhone Duo aims to combine the benefits of both approaches, offering a sufficiently large screen while keeping the controls within reach of the thumb. Some fans have imagined a version called the "iPhone Solo," which would use the size of the iPhone Duo's external screen but without the folding mechanism. However, Apple does not appear to be working on such a device, and there is no indication that a model of this type will be released. Still, the idea raises an interesting question about the current format of smartphones. The trend toward taller smartphones has been driven by the evolution of screen technology, with 16:9 screens giving way to more elongated formats, bezels disappearing, and the Home button being eliminated. Each of these changes has added a few centimeters to the screen size, but not necessarily made it easier to reach controls with the thumb. The iPhone Duo takes a different approach, rethinking how controls are arranged rather than continuing to elongate the screen. This design could offer a new perspective on what a large-format smartphone can be.