The Halo 3 trailer was not the only highlight of today's E3 event. BillG dropped a bombshell announcement as well. "Live Anywhere" is a new initiative to extend Xbox Live to the PC and supported cellphones.

Since Live Anywhere will be built into Windows Vista (along with DirectX 10), you'll basically be able to have cross-platform multiplayer sessions on Live. You could be sitting in front of your Xbox 360 with a bunch of friends, while someone else could be using a PC running Vista on the other side of the continent, and you could set up a multiplayer game.

This is huge. It's a totally unprecedented move, and if executed properly, it could really bridge the gaps in multiplayer gaming. Seeing how successful Xbox Live has become, I'm hoping Microsoft will be able to pull this one off too.

Edit: For more details, check out Engadget's coverage. Scroll down to 3:45PM.