Try to initiate the vast majority of your calls in potential adversary situations. If someone phones you and you aren’t prepared, say the equivalent of, “I’m sorry, but I have an important meeting to attend. I’m already late. What time would it be convenient for me to call back?”
You see, the instant you say something like, “I have something else on my schedule—I’ll call you back!” you’re no longer the callee. When you prepare yourself and do call back, you’re the caller.