This time of year, I pull this prank on my kid.
I carry two phones and I change the contact photo of my work phone to a picture of Santa.
When my kid is naughty or spending too much time on the iPhone, I speed dial it from my other phone.
The results: a good kid for the rest of the day. He actually thinks Santa is calling to check up on him.
Note, this only works on little kids and only around Christmas season.