Well, since there's no official word-- in fact, there are official denials going back quite awhile-- take this note with a few heaping tablespoons of salt.

But Bella Online's Lisa Shea isn't backing down off her insinuation that Halo will be broadband enabled:

It should be out in another month or two, as the main core of the XBox broadband rollout. I am VERY eagerly waiting for that.

Pressed to confirm, she stated:

I'll ask them again to see if they've changed their tune recently ...

Whether it's delusion or inside information I can't say yet, but she certainly thinks she knows this is happening. How it is achievable, I don't know. We've been told more than once that Halo can't be patched in any way; but perhaps the Xbox's software itself can be patched in such a way that is transparent to Halo?