1. sign up for google voice if you haven't already, install apk
2. dl sipdroid from the market.
3. create an account and allow it associate with gv.
4. follow this guide
Note: The guide is only for receiving calls .
when you start the guide you should see GTALK under Trunk, / under inbound, 0 GTalk under outbound. You need this for out going calls.
if ipkalls says you already signed up that means someone already used your ISP ip address.
once you are done you should be able to make and receive calls with 3/4G or wifi...edge is kind of crappy
BTW, you can disable it under settings calls Call Screening and toggle off and confirm...so you dont have to dial 1 anymore just pick up the phone and use you BT headset.
enable 3g in sipdroid settings and now you have a phone :P
This also works on other tabs as well. I tested it on Galaxy Tab Tmobile(simple mobile), Galaxy Tab Sprint(wifi), Archos 101 (wifi), Zenithink wifi, Haipad wifi, and a Wifi'ed G1 works great.