That's a song called "Mbube" - it's a traditional African song that was used as the basis for "The Lion Sleeps Tonight" - you know, the one they sing to Ross's monkey in that episode of 'Friends'.
Anyway, the version of it in the advert is by Miriam Makeba, and you can get it on iTunes.
Just to add - the part of the song they use for the advert is about 48 seconds into the track. It doesn't sound like the advert at first because there's some talking and stuff...