[catherd]

https://wiphone.io/ is Arduino compatible and comes with an audio jack and microphone. It's also completely enclosed, knows how to charge it's own battery, etc. Phone form factor, ESP32 processor.

The back of the phone can be replaced with a custom PCB or breadboard holding your custom hardware. Pogo pins make a connection to the motherboard. The idea is you could carry whatever you end up making around in your pocket just like a phone once you're done, assuming you only put components on the inside of the back cover.

Disclosure: I designed and manufacture it.