Rumor is Phantom Pain is viral marketing for MGS: Ground Zeroes. Why? Because...you know...Kojima.
I've been trying to find a video of Phantom Pain but nothing up yet. I'll post it when I find it.
Edit: Kotaku has the trailer. It definitely HAS to be MGS: Ground Zeroes.
The guy with a burned face, the bandage around the hero's face/eye, the soldiers wearings MGS3 soldier outfits.