Important update: Google Voice will no longer work with OBi devices after May 15, 2014. I would suggest not buying an OBi device now unless you plan to use it with another VOIP service. If you already have an Obi device you can read more about other VOIP providers that OBi supports here.
As I mentioned before, I recently switched mobile carriers from an expensive unlimited plan to a smaller MVNO service called Ting. Since Ting charges according to usage, I have made an effort to reduce my usage. To do that I have been using my Google Voice number more frequently and have found ways to utilize it so that the majority of my texts and calls are essentially free.
Depending on the Android device GrooveIP call quality varied quite a bit - even on the same high quality WiFi network, so I decided to spend a little money and buy an OBi100 VoIP device to try it out for my home. Since Amazon has such a good return policy I figured I would try it and worse case scenario, if I didn't like it, I would just return it for my money back. That way when I know I am going to make or receive a lengthy call I can do so from home on a land-line (old-school) phone.
OBi100 device I bought cost just under $40. You can read all about the features on the product page, so I won't go into detail here, but essentially it is a little box that can turn a regular land line phone into a full-featured VOIP phone with easy set-up for Google Voice. After initial setup making and receiving Google Voice calls is just like having a land line. There are 3 different models that can turn Google Voice into a VOIP, but for most people the basic model shown here will probably suffice.
Call quality has been excellent. I imagine this could vary depending on the quality of your internet connection and your router, but considering the overwhelming majority of positive reviews on Amazon, it seems that this little device works well for most people. The OBi comes with a pamphlet that on how to set up Google Voice, but it is really pretty intuitive and they even have a video and step-by-step tutorial if you need it.
The OBi device works great as an inexpensive landline with Google Voice. It also can send and receive faxes if hooked up to a fax machine or an older computer that has a modem in it. I have used it to send and receive faxes from my ancient Power Mac G5 and it works perfectly.