A seems too abrupt to me.
I agree with you that C and D are a waste of breath and are somewhat annoying. C would be fine if the call is being answered by a switchboard operator who only directs calls. John Smith speaking is totally unncessary.
D is *very* annoying. I don't want an advertisement when I call a business. I want them to just help me with whatever my need is.
I've made it my policy that if I'm waiting in line to be served and the sales clerk thinks it's *more* important to take a telephone interruption than to serve me I'll put down my purchase and walk out of that store. Telephone customers do not have any more clout than customers who are in front of you.