Huh, apparently (see other comments) it's not possible on un-rooted Android for some reason (although I'm finding it hard to see how it could be possible to read from bluetooth mic and write to on-board speakers but not be able to do both at once, but then I know nothing about the APIs involved). So, now I need other ideas for how to amplify my voice. I could put a headset in the helmet and then if I want to talk to someone I could just phone them and their phone could be the speaker, but that seems... unnecessarily complicated. I mean, it should work. But holding a phone call open just to talk to someone right in front of me? Ugh. Or I could put a whole phone inside my helmet with the mic near my mouth and use an external bluetooth speaker. But then how would I control the phone? Ugh, I don't know. I was hoping to be able to rig something up quickly with stuff I've already got before next weekend but I'm guessing I should forget going to that particular event after all, oh well. Any ideas?