Just bought
one of these.
~$50 gadget, that allows you to use a Google Voice number to place/receive calls using a normal phone setup. No charges at all past that initial purchase, unless you add E911 that GV doesn't provide, for $10 - $15/year. If Google Voice sound quality turns out to be less than needed, you can plug into any other SIP provider, which typically run $50 - $100 / year.