@Linkat,
I can understand prioritizing bosses, but that doesn't excuse him from contacting you. He can interrupt long enough to say "Linkat and I have a call scheduled; let me tell her I'm busy so that she's not waiting on me."
If I were you, I wouldn't wait more than 10 or 15 minutes, though. And I wouldn't let 'em off the hook for the call,
and he needs to accommodate your schedule.
I'd also suggest to him that he needs to notify you if he's tied up (preferably by having a co-worker call the conference).
Finally, if the problem is chronic, I would hope that they are in a different time zone and you can move the conference call to a time that's uncomfortable for them....