What servers can you say anything

In WoW you can theoretically say anything unless you have a trial account, where some channels are muted.

That said, all servers are monitored regarding racism, offensive language, item spam, Chuck Norris jokes and the like. If you are reported by 10 or more people for this, you are muted for some time, and if Blizzard's investigations find you guilty of the above, you can be banned for anywhere from a few hours to permanently.

In general, it is best to act civilized and intelligently when using the various chat channels in World of Warcraft, because it not only prevents you from running into trouble, but also shows you know how to act socially responsible.