I started as all good projects should, with research.  I found a document http://www.splorp.com/pdf/stowawayhwref.pdf that shows how to write drivers for they keyboard.  This luckily also shows things like the keymap, communication protocols, etc,

I originally tried interrogating the keyboard using RS232 many years ago but failed, most likely due to inexperience at the time.  Retrying now, I found I can't get reliable connections to whats left of the soft ribbon cable and opted to remove the existing circuit all together.  

My current thought is to use something like the CYW20730 keyboard circuit with integrated Bluetooth which is just about perfect.  In order to do this I needed to determine the physical keymap.  I carefully disassembled the keyboard and took pictures of the traces.  I loaded the pictures into Gimp along with a transparent picture of the keyboard in order to match up the two, and got to work manually tracing each line.  

The result of this was three separate keymaps.  Studying the keymap from the manual, I was able to see that they were combining the three together Tetris style with some bridged pins.  Most likely to fit the matrix limitations of their controller.

The final keymap with pin labels is as follows:

(Note, pins are labeled by bus, left to right as the cables lie in operation, i.e 3.1 is the first line on the third bus [far right segment of the keyboard])

My next steps will be to design a physical circuit to replace the existing one utilizing the CYW20730.  This will involve making a model of the current board footprint then using KiKad to generate all the required traces to the controller.  Cypress seems to have pretty good chip programming software, but I will need to learn how to do that too.  

Future work:

design PCB

Program Cypress chip

Figure out how to attach adhesive ribbon cables from keyboard to a PCB

install a tiny LiPo where the handset used to sit so the unit still closes flush.