Your readers seem to take this literally, and indeed you have given examples: The doctor, mechanic, etc. Still, this can apply to most of us. Human nature being the way it is, we initially try to please until we suddenly feel that we have one telephone number or e-mail too many. We may also feel that we have given our details and goodwill one too many times also. Life, viewed from a particular standpoint, can be quite hectic and so sooner or later we will inevitably use some form of defense strategy to protect ourselves. For the professional, this is heightened.
My considerations in calling, in light of the above, would be to prepare for some form of excuse coming from the sometimes unshifting secretary. I would also consider the persuasive appeal; conveying the necessity of the situation; have I got the time or patience that may suddenly become necessary, and yes, the use of assertive empathy in all situations. Above all, I will strive to be guided from within.