A pair of video commercials for the gadgets, which were unveiled yesterday in Cupertino, California, feature the duo's hands and voices.
In a 30-second clip, the pair can be heard humming to the theme of '2001: A Space Odyssey', 'Thus Spoke Zarathustra', while the phones' features are displayed.
In the other spot, Timberlake and Fallon talk about what people can do with the phones.
Apple's CEO Tim Cook announced the release of the two gadgets as well as Apple Watch in a grand event which was also attended by U2.