This isn't really a guide, but best forum I found for the information (note the *news* tag =D)
Pre-TBC WorldDefense was reserved for players of rank 11 or higher. In the 2.2 PTR, this channel was opened up for everyone, probably un-intentional, but it was never fixed.
For those of you who don't know, there is a channel called WorldDefense, similiar to LocalDefense, except it will alert you to attacks on allied (not just alliance, I mean, your allies) forces all around the world. IE, you're in Shatt, someone attacks Sentinel Hill, or Crossroads, you'll know about it. Looks the same as a LocalDefense call..
Anyways. Pre-2.0, only rank 11 and above players could speak using this channel. Everyone else was limited to observation. I noticed in 2.2 PTR that everyone could speak, regardless of rank. So, tonight while I was looking for minerals, I decided i'd give it a shot, and sure enough, it's still open to everyone (on a live realm). The character I was playing was a post-TBC 70, so he has NO rank, yet still able to communicate.
I logged in 2 of my alts, a Knight-Lieutenant, and a Blood Guard, and it was the same on both sides..
This will probably just provide more means for spam, but still, useful information, IMO.
Hope some of you find a productive use for this information =)