Same 503 error. I had an older OBi100 box, deleted it from dashboard, got out the OBi200 that I had bought 2 months ago as a backup, configured that and getting the same 503 error on outgoing phone calls.
Google Voice (app) on my AT&T iPhone works fine, leading me to believe this is OBi specific
FWIW, inbound calls do not work either. Earlier today (March 27) the phone worked fine. This evening, perhaps around 630pm EST my cell phone rang from my GV number but the phone connected to OBi100 did not. At 8pm I have a GV rule setup to stop getting calls pushed to my cell phone, and at 8:03pm I got a Google Voice voicemail notification, so the service is still working fine, just not passing through OBi