Thanks for the reply giqcass. I just tried your suggestion, and the result is the same, about 8 seconds of silence after dialing, then a fast busy. Note that the problem remained the same even right after a factory reset, before restoring any saved config. The digit map is factory default at that point.
One thing I didn't mention before is that the OBiTALK1 call state is briefly "turn-alloc", whatever that means, prior to ending on "lookup" for most of the time before the busy signal. This happens on dialing any OBiTALK number, including using your speed dial test. The call log always shows the outbound call, but never "Call Connected". So it is not that the OBi is refusing to attempt the call, it just doesn't work. I don't think there would be a call log entry if the call didn't pass digit map processing, would it?