To clarify a bit, you can go into your account send yourself a "recruit-a-friend" invite, accept it and make a new account (free trial) that is linked to your main account. When you upgrade WoW from trial to full for $5 your main account will get a month for free (~$15 value). That is if I'm not mistaken. This will get your new character, say a worgen or goblin, x3 gained xp if you multibox accounts (fully legal, Blizzard wants your money) and have them quest together.
If you want to take this one step further you can buy 60 days of game time on that newly made account and you'll get a very unique looking two seater rocket mount. After you do this once you can cancel the buddy account and let it die out after the time expires, but you still keep the mount.