though one can use any old Android that does Wifi to do SIP, it has its charms to use less capable hardware for this with less software complexity. I don't kno

though one can use any old Android that does Wifi to do SIP, it has its charms to use less capable hardware for this with less software complexity. I don't know that many projects of this category: the "ZeroPhone" was based on a rpi-zero and active 2017-2019, the "WiPhone", a ESP32/Arduino based device, is still ongoing.