A trivial Google search reveals Urban Legends: Cell Phone Popcorn
Update #1: It turns out the video was indeed part of a viral marketing campaign for [REDACTED] Systems, makers of Bluetooth headsets.
Update #2: [REDACTED] Systems CEO Abraham [REDACTED] reveals how the cell phone popcorn trick was done.
Stuff redacted because I don't like being a stooge for corporate marketing weasels
Update: In a comment below, Oddthinking points out that the video referred to in my answer is not the video referred to in the claim.
One explanation of the video in the claim is that the makers of the video in the claim may have simply used the description of methods provided by the makers of the video referred to in this answer.
I would delete this answer but it may have some tiny value in illustrating that Youtube videos are not "indisputable" sources of truth.
Physicist Debunks Cellphone Popcorn Viral Videos
The clever parlor trick (see embedded clip) looks amazing enough, but there’s a hitch: It’s not physically possible, according to University of Virginia physics professor Louis Bloomfield.
See also Snopes: Cooking eggs with cellphones
In October 2005 the television program Brainiac, a UK-based science show, aired an episode in which they tried cooking an egg by placing it under a pile of 100 cell phones. All they ended up with was an unwarmed, uncooked egg:
This joke is 13 years old.