This is the first I heard of this, but apparently there was a rumor going around that Bungie was developing a version of Halo for Nintendo's Game Boy. Today official word came from Bungie that: "There is no Game Boy version of Halo planned, and none in production."
Bungie Software today denied rumors of a Game Boy version of Halo, publishing a brief note to that effect on its official website. Though reports from seemingly reliable sources claimed a handheld version of the popular Xbox first-person shooter was in the works, Bungie had this to say:
"Recent internet reporting has suggested that a Game Boy version of Halo is in the works. We can officially lay that rumor to rest. "There is no Game Boy version of Halo planned, and none in production. It's very unlikely that such a version would ever happen for all the obvious reasons, and the less obvious reasons, that the ColecoVision talks fell apart and The Bandai Pippin version is taking up all our development bandwidth..."
News source: 1UP