another thought. I dont know how many phones you have, or how you have things set up, but years ago, we switched from a landline to a voip service. What I did was, I completely disconnected my home from the verizon service (2 little wires). this can be done from their main connection box, or somewhere else. just make sure that you have no connection going back to the company. Then I took a regular phone cord, and plugged it into the phone jack on the wall. It now powers all the phones in the house. We have one phone in just about every room of the house, which makes it nice because if someone calls, there is always a phone near by. I am just saying this, because i dont want you to think that you can only have one phone hooked up to this device. It is still just one line though.
right now, I am kind of doing the same thing. I bought one of their 202 models, and if all is good, I am going to switch my phone number from phone power to this, and sign up for phone power as a provider. I am told there are some limitations to this, but i guess, if you sign up with another company, then what happens is if one goes down, then the other company takes the slack. and you can set the primary provider as which ever one you want. So if you only have goggle voice, then you are relying completely on them, but if you sign up for another company, like phone power, then if google voice is having problems, then it will switch and try phone power to get the call through, and vise versa. So my service, I am guessing, in the end, will be the same as I have now with phone power, just a much lower bill. going though this way, it ways that the service, with phone power, is about $60 a year, while going though phone power by itself, cost me over $200 with taxes a year. a major savings.