(Google Translate from French) The phone uses an ESP32 at its core, with a SIM800L GSM modem to interact with the cell network, including retrieving the system time.

The TTGO is a small ESP32 board with an ST7789V 1.14 in (29 mm) TFT color display, available from your favorite Shenzhen market supplier. This platform is perfect for all kinds of niche applications.