Yesterday, I came across the baresip program: an extremely basic, command line, SIP client. After messing around a bit with the program, I found that it had major potential to be the client that served the radios. I set up a test which utilized the URIx-Util lib and snagging the stderr of the baresip program. After much cringing at how gross this code was, but proving the concept worked, I was very happy and began to plan how to better get the DTMF events out of the SIP client.
Thus, I began the process of learning a C based module API that has no (real) documentation associated with it (at least that I could find).
After a few hours of poking at it, giving up, realizing a better way to do it, more poking at it, etc., this pull request was born.
Here is the info from the pull request: