I have to laugh at myself.
I live in an area where you have to enter the area code to dial locally. This has been in effect for several years. All this time (well over 2 years) my OBi has been provisioned with the optional 7 digit dialing area code filled in. It didn't occur to me until just now to actually try it while I was looking at my GV settings. Lo and behold it works for both my SP's. duh
