Tvov, I understand your situation. I was a contractor for years ... and yes, it would and does annoy me when someone answers a phone while we're talking, especially in a supply yard, and then goes and takes care of that problem while we sit and wait -- when that happens --- this is me leaving ---
But to the point: my post above was more about a person returning a call ONCE, and then expecting that to be a responsible way to do business. IF it's true, that a person like yourself can't answer often due to work, then return a call to a potential client MORE THAN ONCE. When a business returns my call, and says, call me back (AGAIN), I don't, I go find another business. My time is as important as anyone else's, and to expect me to continuously return a call to a number that is never (or infrequently) answered makes no sense, especially when my return call once again gets a message.
Once a potential client has initiated contact to a business, it's the responsibility of that business to call enough times to get the person, not just once and assume that is sufficient. It's not sufficient, in fact, it's rude and unprofessional.