Pure awesomeness! I've spent a while trying to figure out how to:
-- Turn my Archos 80 G9 into a full-featured phone
-- Having the ability to talk via A2DP Bluetooth headset instead of the built-in speaker
I accomplished both today... and the best part is... all calls and texts are FREE (considering you have a wifi or 3g/4g data connection available). It all involves Google Voice, Google Talk and Groove IP (or Groove IP Lite if you're only using it for wifi calls).
First, create a Google Voice account (if you haven't already). Make sure to download the Google Voice app on the Android Market as well, as this will be your SMS client (unless you prefer your SMS to be sent to you via email). There may be other SMS porting apps out there as well.
Go through the motions to get a Google Voice number. You will NOT need to keep the phone number associated with your Google Voice number, so as long as you have it initially activated, you'll never have to worry about forwarding calls to that number (I actually made the mistake of buying a Skype number for the forwarding feature).
On a PC browser, access your GMail account (or make one if you don't have one) and go down to chat and call a number with it. You're only required to do this once. After you hang up, disable chat on all computers that have your GMail account signed in except your G9.
Go back to your Google Voice settings and forward all calls to your Google Talk account.
On your G9 (or any other Android tablet you have), download Groove IP ($4.99) or Groove IP Lite (Free - you can read about the differences on the Market).
When Groove IP starts, provide your credentials for Google and you're free to start sending/receiving calls and texts!
Now for Bluetooth! I recently bought a GoGroove Airband wireless stereo headset (yes it's bulky, but I like listening to my music, too!) and it works fine with listening to music AND phone calls! Make sure your headset is A2DP compatible, or it won't work!!!
Once your BT headset is paired with your device, open Groove IP and go to Settings > Troubleshooting and select WiFi Tablet. You can now listen to your music AND phone calls with the headset instead of looking like a weirdo holding up an 8 inch tablet to talk on the phone!
OPTIONAL: While you're on troubleshooting, you may want to select the High Perf WiFi Lock option, as I'm not sure if the G9 goes into a power-saving mode when you turn the screen off. If your WiFi's off, you're not gonna get any calls! Hope this helps someone from a month's worth of research and about 100 bucks in wasted money on Skype and about a dozen Android dialers and clients!