Don't trust everything you hear over xbox live....
Microsoft disabled the entire Original xbox Live service, meaning no original xbox games with live content can now be played online.
Halo 2 is an original xbox game = no live
Iv read this so many times in multiple different places and everyone bases their facts off of Halo 2 no longer being live supported while no original xbox games still have live support. Halo 2 online live basically got caught in the crossfire of a descision made at a much higher level. Not being able to play halo 2 on live anymore is a result of this and not any direct action towards disabling only the Halo 2 live service...
I find the facts get lost most likely because nearing the end of the original xbox live service Halo 2 had the highest percentage of players for original xbox games with live content. So when the service was disabled many looked at it as just losing Halo 2 and not realizing that the entire original service was disabled.