The latest is the TTGO T-Call, an ESP32 breakout board that also has a cellular modem. Yes, it’s only a 2G modem, but that still works in a lot of places, and the whole thing is $15. On board ...

The custom PCB plays host to the essentials — an ESP32-S microcontroller, AMS1117 3.3 V regulator, a SSD1306 OLED, and a couple of buttons. This lets the user navigate through a simple menu ...