Ironically a common writing technique is B->C dialog.

Basically cutting out the preamble and post dialog. Most times even in my writing I include “Hello” since that would stand out, but generally get right to the point.

You see this a lot in movies too, if done well it blends in since your scene is focusing on the action and not rambling on.

There are exceptions (teens talking may include a “no you hang up” trope for comedic effect) but that’s used sparingly.