Can I use Google Voice as the VOIP provider? I read that article and couldn't tell if Voice is used in addition to another VOIP service, like Ooma.

It blows my mind that the current Cisco ATA is $150+.

For the service I am building (havenphone.com) I used Grandstream HT801 with success with voip.ms. I don't love how easy their cloud can take over the device though.