In a nutshell, it provides two-dimensional scrambling: time and frequency domain and able to connect to telephone / radio link.
Quite interesting and good looking device, in my opinion.
Thinking a bit over, I decided that it would be nice to have that thing nowadays, but with VoIP supports and capabilities to work with SIP phones.

So, I've started to create prototype...

For the first version I defined the following features:

• It should be a software based solution with VoIP support. Capable to run on single-board computers.
• Provides SIP registrar functionality (for local SIP phones), and SIP gateways (for connecting to external PBX).
• Key exhange and screambler should be work over analog (PSTN) telephone lines, as well as over VoIP networks too.