Google Voice is a strange creature; no one is quite sure what Google is planning. Google use to allow regular sip connections to Google Voice, then they dropped it, they purchased Gizmo and everyone thought that was going to be the way then Google abruptly ended Gizmo. All sip connections to Google Voice was blocked. I never understood the whole one way telephone; what good is having some telephone service that is only incoming? Oh, I got a call while I was in the loo and a voice message saying it is urgent, please call back. Damn, to call I have to use my regular phone.... sorts of negate the whole purpose of having a Google Voice telephone number. Maybe the idea with Google Voice, which Google purchased from Grand Station, was to somehow tie it to advertising; which has always been Google's main revenue stream. Then the whole Hang Out mess which didn't pan out along with G+. Google just never did get social media right.
On its own, there is no real value in Google Voice; mobile phone plans are fairly cheap these days. The value in Google Voice would only be if you had a cheap way to use it like you would any other VoIP service. Many ISPs are now offering bundle deals on television, internet, and phone service for around $100 a month. Then comes the agreement with PolyComm which turns Google Voice into a regular VoIP provider with PolyComm providing the devices. Not a bad deal, for one payment of around $70.00 you have lifetime free VoIP service through Google Voice. PolyComm was the only way to get true VoIP service with Google Voice because Google blocked any other connections to the GV servers.
Now what many don't realise is that Google does collect termination fees. However, calls have to be made. I wonder if the deal with PolyComm was to have a real VoIP service; web and phone apps does not make a real phone service. I have a feeling that Google does not want to be a real VoIP provider; which is why they never offered any sort of paid connection to GV; like in a bring your own ATA plan. I don't know the VoIP regulations; I am sure their are some. Also, remember if you are a telephone service provider, then the FCC regulations step in. I don't think GV is classified as a telephone service provider but I don't know the rules and regulations.