Well, I'm not an HTC representative, but I believe HiTech wrote this himself. He ran a beta for a couple of months with AH Voice as a stand-alone application, and then integrated it into AH itself. I believe he wrote it from scratch using the Microsoft Direct X API's... but that's just my guess. I believe that there are some voice comm API's built into the Direct Play suite now, and I bet he wrot it to those.
And yes, IMO, HT deserves a big for this great feature.