That will be extremely difficult as the English AMBE specifications
are proprietary and
undisclosed unless something has changed. Reverse engineering with
be legally discouraged
I would imagine.
The specifications from ICOM for the rest of the system are open. So
you will able to send
(say) SPEEX encoded speech (hoorah for SPEEX) along the D-Star system
but be unable
to communicate with their end users doing AMBE.
I got this directly from the Icom person promoting the D Star system
at Dayton 2004 in the
technology forum.