I join in with the others that say it's a repost, this is really old.
A friend did it back just when TBC came, had a level 1 Blood Elf Priest and his main was a Night Elf Warrior, pretty cool stuff.
Nowadays, I think you have to make it a bit more advanced, since Blizzard knows people try to do this.
Heard that a good way is to make 2 new characters, whisper from 1, the GM will tell you "please delete this character after we are done talking, since it's the opposite faction."
Then you do as the GM says, but you still have the other one left.
It is a pretty funny thing though, if you get ganked 10 times, you can just log and please ask the person to stop, or yell at them or what ever. x]