I hear what you are saying. There are nights when Nathan asks for his dad (last night he wanted to know when Dad was coming over, I told him it wasn't Daddy's day, he said but Daddy ALWAYS comes over every night...), but there are nights when I am sure if I didn't bring it up, they wouldn't ask.
The comment about us calling him came last summer. Dan was in selfish mode and he would call at 9:30 and be upset that the kids were already in bed. The 'set' bedtime is 8:30; that is the norm. But on occasion if we have traveled to visit family, or went out to dinner after karate, etc., sometimes it varies from that. But not by much.
Anway I realize that I don't need to have the kids call Dan on "my" nights. I guess it is just the pattern we set up before we separated and neither of us has changed it at this point.