This year's ad prank is Trust Banners that gain "consumer trust through high frequency (90fps) banner adverts which stimulate specific regions of the visual cortex (Visual area V5/MT) producing instant effects on consumers."
Turning black and white TVs into color sets by wrapping them in nylon stockings must be the best media-related April 1 hoax ever (Orson Welles's War of the Worlds was on Halloween so it doesn't qualify). Above is the original broadcast on the Swedish TV back from April 1, 1962.
Among the pranks that would actually make sense to implement for real is last year's announcement by XM radio that it is launching a new channel entirely powered by podcasts.
The always adorable Google added a new function to Docs this year that creates a blank document with an outline of a paper airplane.
Remote Control Jammer Chip Activated By Commercials