The hardware is relatively simple:

The back of the phone can be used as a prototyping area, or to expand the phone capabilities:



And the assembled phone has a see-through front, because we like hardware:

Currently debugging the (hopefully) last prototype electronics. The phone can already be used with a commercial VoIP provider, and we made a bunch of add-on boards, which we call daughterboards.
Future plans include MicroPython, OTA firmware updates, and producing real phones people can buy.