The title pretty much says it all, and it's not one of those lame pseudo-open betas where you get in if you pre-order the game, thus defeating the object of the beta being open. Oh no, Activision is becoming the light to oppose EA's evil. All you have to do is go to callofduty.com and register. That's it.
The beta is going to be released within days as far as I understand it, and 360 owners will get their version of the open beta shortly afterwards.
After being impressed so much in the week I have owned CoD4, I'm almost certainly going to be participating in this one, and I'll post up a review of some description I suppose just prior to the game's actual release date, November 1st.