Edit: You can pretty much disregard this post; Google announced that they are ending the service that allows for the Obihai devices to make free calls. Keeping it here for historical purposes.
I’m a big supporter of all the different Obihai VOIP devices. I’ve had an Obi110 since they launched for $50. For the uninitiated, these devices connect to various VOIP providers and allow for voice calls via an internet connection (there is a NIC in the device). The big selling point (especially at launch) is that it can interface with a Google Voice, which means free calls (no 911 service, but there are workarounds). My problem deals with the fact that my Obi device has one Google Voice number, and I have a separate Google Voice number for myself. Google Voice will not forward a call to a Google Voice number.
The solution is to sign up for a Callcentric account. You can then enter those credentials in the Obi administration page, and test the number that Callcentric provides. Then, take that new number and add it to the Google Voice settings page for your personal Google Voice account. Now, when somebody calls your personal Google Voice number, your Obi device will ring as well.
Offsetting as much voice communication as possible to free solutions allows users to get along with a much, much cheaper mobile plan, like Lycamobile or the T-Mobile $30 plan (which is what I use).