I very vaguely recall reading something somewhat similar on here a long while back (like a year ago) something about phoning and asking about diapering, and whether the change table is near a window. I believe another daycare provider posted something like that on this site. I wonder if it is the same creep...or if there are multiple creeps phoning home daycares about such things.
Any chance a call to the police station (non emergency number) would be useful? They might be able to track it, despite it being a private number.