>>last night we had a PG&E power failure. today, after power was restored, the phone service is messed up. incoming calls get a message saying number "can't take your call now". outgoing calls get a busy signal.<<
Hope by now you're back online and everything's working, but if not (or just for future reference), I've found that these kinds of situations often result from timing issues, when one device (like your ATA) comes online faster than another device (like your router) which it's dependent on. The router, being a more complex device, takes longer to come online than the simpler ATA box, so if power is restored to both devices simultaneously, the router is not online yet when the ATA is ready and expects it to be.
Try unplugging everything from your AC power, then after a minute plug the router back in. Allow it the full five (or so) minutes to come online, and then power up the ATA. When it comes online and tries reaching out to the Metaswitch, the router will be ready to route the handshake.
The ATA ought to be smart enough to recognize when upstream communications isn't ready, and pause for some reasonable amount of time (say, 20 seconds) before retrying. If it keeps failing after some reasonable number of attempts, it should be smart enough to reset itself before trying again. (Maybe that is what it's doing, but I've encountered timing issues and "deadly embraces" enough times to suspect the Grandstream device is less than fully robust.)