Styles, 18, a member of band One Direction, sent the song "What makes you beautiful", sung in a country and western version for Swift, 23, reported MTV online.
"Even though they were apart on Christmas Day, he wanted to make sure she'd be thinking of him. The singagram was an ideal present. She has a great sense of humour. He knew she'd think it was hilarious," a source said.
Styles and Taylor did enjoy a chat together over Skype on Christmas Day.
"Harry and Taylor can't get enough of each other. Any moment they can spend together, they do. But Harry is also very close to his family. He wanted to be back home with them for Christmas," the source added.