I don't know if any of you guys follow xda-developers, but there's been a few discussions over there about the AN-21U, android head unit. Apparently, this unit we've been discussing in an AN-21U in a fancy faceplate. And while that seems like just "nice to know" information, it is more than that. It's more because some of the people over on xda-developers are modding their units. In fact, they've figured out how to hard-wire an external microphone to their units.
http://forum.xda-developers.com/show...4&postcount=46
I don't know if that would work for these units, but maybe it would. Somebody would have to take theirs apart to get to the board in the device and look for those two mic connectors on the board, then connect a mic to test it. IMO, the next step would be to wire that to the in-car, Onstar mic.