Seems like we need Miss Manners here!
If someone calls frequently, I would definitely fix a time that suits both parties and the time difference.
I have learned through bitter experience to start the calls I make by asking "Is this a convenient moment?" or "Do you have time for a chat". This gives the other person an opening to ask when they may phone me back, if my call is inconvenient.
Havemercy, I know exactly how you feel: once when something horrible happened here, I phoned a friend who the minute she heard my voice said, " I haven't time now" and put down the receiver. That taught me to start with," I really need to talk, this is a ghastly day," if that is the case in the hope that a friend will either make time, or arrange to phone back as soon as humanly possible.