Apple has begun airing a holiday-themed iPhone 4 commercial. Entitled “Under The Covers” and set to “The Christmas Song” by Nat King Cole, the ad—shot in the style of Apple’s original FaceTime iPhone 4 spots—shows a mother and son on a FaceTime call with Santa. As the mother leaves the room, the young boy covers up with his bedsheet and continues talking to “Santa,” who is revealed to actually…