You have to have Internet service for this to work. I have Comcast Internet. I plug the Obi100 into one of the Ethernet jacks on my Netgear WiFi router. Then I plug my cordless phone's base station into the Obi100.
You don't need a computer for this to work but it is easier to access some of the Obitalk features using your browser to reach its configuration screen.
You don't need a third-party VOIP service provider for an Obi phone to connect with another Obi phone over the Internet but that's a pretty limited reach.
I had the same dilemma. Was using google voice w my obi. So now I use my obi100 with Vestalink http://www.vestalink.com/pricing/?plan=basic
$75 for two years
For those who are confused—— obi100 is merely a piece of hardware. VOIP hardware-—electronics
You still need a VOIP provider to route your phone calls over the internet. I was using google voice for this but now use Vestalink
Vonage gives you one stop shopping but for a higher price, They supply the VOIP hardware
+
the call routing over the internet
Walmart Basic Talk is 10$ a month is the same one stop shopping and does about the same as Vonage at $10 a month/ Vonage has more features I believe