According to a usenet post (http://groups.google.com/groups?hl=en&frame=right&th=c3af263feb5fbb06&seekm=m31yv9xrjg.fsf%40duchess.twilley.org#link1) That thread :P

http://www.synergy-gps.com/M12_Oncore.html

Is the reciever used in the OnStar system. Don't know how useful that knowledge is, but hopefully it's somewhere to go off of.