Thanks for the prompt answer that fixed the issue! I did not realize that their was a difference between the Circle of Trust and Trusted Callers.
The only reason I am using this method, at least for now, is that I don't have a VOIP service provider on the one OBi device whereas I do have one set up on the other (Google Voice), so it enables me to place calls. I don't think that I can register the same Google number on two devices, but do you know if any other VOIP services permit registration on two different devices?