I am having exactly the same problem all day today. I can't place or receive calls. It's been working well for over a month without any problems.
I've had a number of different symptoms. Tried setting my google voice password on the obitalk site. I also deleted my google voice account and the device and readded them. I rebooted the device, router and cable modem. Symptoms have been:
1) When dialing out voice says,There is no service available to complete your call
2) When dialing out voice says, The number you dialed xxx, was rejected by the service provider: reason 500
3) When dialing out, after long delay get noise on the line and nothing else.
4) When dialing in, nothing - goes to voicemail on gvoice