Note from the author: It's very hard to find the correct ESP32 dev boards now with the resistors, they are sold out everywhere. The ESP32 module of the current version does not have an OTG pull-down resistor, and a U-type connector is needed to solve this problem.    

U-type connector：https://www.aliexpress.us/item/3256806668421477.html. Choose"Color: C female-C-C"

kv4p HT is a homebrew VHF radio that makes your phone capable of voice and text communication completely off-grid with at least a Technician class amateur radio license.

The radio simply plugs into the USB C port on your Android smartphone and transforms it into a fully-fledged handheld radio transceiver. It's completely open source (GPL3): the Android app, ESP32 firmware, PCB designs, and 3D printer files.

It's small enough to fit in your pocket and take anywhere, and since it has no internal battery it's the perfect emergency radio to put in a go-bag or your car's glove compartment.

See https://kv4p.com for instructions, open source code, and more information!