Would love to start with open hardware, but what I got on hand is a Raspberry Pi and 2 cheap usb soundcards. It should be easily replicated using only open hardware. See all architectures supported by Debian.
It will have at least the same basic UI features as the USA Western Electric Model 2500 telephone but with some extras needed for ZRTP: more keys and a screen to show the SAS code.
Awesome project! Unfortunately the link to download the raspbian img file is not working. Is there an alternative link or link for the full code to this project?