I can tell you from listening to our program coordinator, that multiple phone calls will annoy some coordinators...and then you suddenly get dropped from the backup list.
But really, backup interview spots are VERY long shots to begin with (if you know what I'm saying). And if a candidate has a stellar application, there will always be an interview spot for them.
Oh, so bottomline: it's okay to call the program coordinator, but not so much that they get annoyed (which varies of course from person to person).