➀ This article introduces the design of the world's smallest programmable smartphone, the IndusPhone, which is only 3cm in length. It outlines the selection of components, integration of features like 2G and 4G SIM card support, Wi-Fi, and touch display. The article also covers the design of the basic UI and testing of the GSM module. ➁ The IndusPhone is designed using the IndusBoard coin, which is compact and includes many I/Os and sensors. The UI design includes features for making calls, messaging, and sending messages. ➂ The article discusses the integration of the GSM module, the code for testing GSM functionality, and the construction of the circuit diagram.