Olivia Olson (born May 21, 1992) is an American singer and actress. She is known for her role of Joanna, singing "All I Want For Christmas Is You", in the 2003 motion picture Love Actually. She was a cast member of Disney's animated series Phineas and Ferb and supplied the voice of Vanessa Doofenshmirtz. She also sings many of the songs in this Disney series, including the duet "Busted!" with Ashley Tisdale. Still in her early teens, she has written songs for Phineas and Ferb