I have done a couple of tests with configuring my OBi110 to reject calls. One was to turn on DND. The other was to craft an X_InboundCallRoute that did not route anywhere.
In both cases, calls to my OBi did not appear in the call history, and syslog only said 486 Busy Here.
It would be helpful in troubleshooting to log rejected calls so that we could tell exactly why a call was rejected.