Smash Mouth's version of 'Under Pressure' appeared in the film Zoom. While this is just a clip, it has been confirmed that the whole song was recorded, yet hasn't been released on the soundtrack, nor on any Smash Mouth albums or singles.
On the official Smash Mouth forum, it was said that on the full version Steve Harwell (Smash Mouth's lead vocalist) sings most of David Bowie's parts... while Greg Camp (Smash Mouth's ex-lead guitarist) sings most of Freddie's parts. They also switch a lot of the lines.