yekke2: there is no chiuv to call anyone “rabbi” who has smicha. If you dont want to call so and so rabbi, unless he is the rov of the community you are in there is no halachic basis to demand calling him rabbi. If there is a need to maintain an equal standing with someone, for communal or professional reasons, it is completely valid not to call him rabbi. I have asked my rabbi this question as well.
regarding the mitzva to honor a talmid chacham, that does not include many of the people who have some sort of smicha today and does include many people who do not have smicha. the talmid chochom of the gem is very dif to the talmid chachom of today.