“What's Your Number?” features a guest appearance by Tim Armstrong, the guitarist and singer from Rancid, who gives the track a punk flavor.
The song is based on a re-recorded version of the bass riff from "The Guns Of Brixton" by The Clash, giving it a unique blend of hip-hop and punk rock.
The lyrics begin with a scene in which the narrator notices a woman in a club who stands out from the crowd with her charisma and style. It's less about superficial pick-up lines and more about a mixture of curiosity and fascination that she triggers in him. The title "What's Your Number?" alludes to the attempt to make contact – a metaphor for the interest in finding out more about her, be it her telephone number or simply her identity.