I use my OBi200 with Google Voice and it's completely free!
Yeah, that's what I was going to do. At the time I set up the OBi Google was saying they were going to stop Google Voice, plus I needed to port a normal landline number, which was an added hassle. I actually use GV for our mobile phones. No need to pay ridiculous prices per text message, free Wi-Fi calling, and we can port our own phone number as needed.